class (n.) Look up class at Dictionary.com
c.1600, "group of students," from French classe (14c.), from Latin classis "a class, a division; army, fleet," especially "any one of the six orders into which Servius Tullius divided the Roman people for the purpose of taxation;" traditionally originally "the people of Rome under arms" (a sense attested in English from 1650s), and thus akin to calare "to call (to arms)," from PIE root *kele- (2) "to shout" (see claim (v.)). In early use in English also in Latin form classis.

School and university sense of "course, lecture" (1650s) is from the notion of a form or lecture reserved to scholars who had attained a certain level. Natural history sense is from 1753. Meaning "a division of society according to status" (upper, lower, etc.) is from 1772. Meaning "high quality" is from 1847. Class-consciousness (1903) is from German klassenbewusst.
class (v.) Look up class at Dictionary.com
1705, "to divide into classes," from class (n.) or French classer. Sense of "to place into a class" is from 1776. Related: Classed; classing.
classic (adj.) Look up classic at Dictionary.com
1610s, "of the highest class; approved as a model," from French classique (17c.), from Latin classicus "relating to the (highest) classes of the Roman people," hence, "superior," from classis (see class). Originally in English, "of the first class;" meaning "belonging to standard authors of Greek and Roman antiquity" is attested from 1620s.
classic (n.) Look up classic at Dictionary.com
"a Greek or Roman writer or work," 1711, from classic (adj.). So, by mid-19c., any work in any context held to have a similar quality or relationship. In classical Latin noun use of classicus meant "a Marine" (miles classicus) from the "military division" sense of classis.
classical (adj.) Look up classical at Dictionary.com
1590s, "of the highest rank" (originally in literature), from classic + -al (1). Classical music (1836) was defined originally against romantic music.
[I]n general, as now used, the term classical includes the composers active in instrumental music from somewhere about 1700 to say 1830. Hence the list includes among the great names those of Bach, his sons, Haydn, Mozart, Beethoven, Clementi, Dussek, Pleyel, Cramer, etc. The next step beyond the term classical is "modern romantic," the composers of which school may be taken to include all the writers for pianoforte from about 1829 (when Mendelssohn published the first "Songs without Words") down to the present. The term romantic in this sense means strongly marked, extraordinary, intending to tell stories and the like. ["Music, Its Ideals and Methods," W.S.B. Mathews, 1897]
But already by 1880s it was acknowledged the term had a double sense: Music that had withstood the test of time, as well as music of a style contrasted to "romantic." Later (early 20c.) it was contrasted to jazz (in this sense more often with reference to the orchestras than to the music itself). Still later in contrast to popular music generally (mid-20c.).
classicism (n.) Look up classicism at Dictionary.com
"classical style in art or literature," 1830, from classic + -ism. Related: Classicist.
classics (n.) Look up classics at Dictionary.com
"Greek and Roman writers and works," 1711, from classic (adj.).
classifiable (adj.) Look up classifiable at Dictionary.com
1820, from classify + -able.
classification (n.) Look up classification at Dictionary.com
1772, "action of classifying," noun of action from Latin stem of classify, or from French classification. Meaning "result of classifying" is from 1789.
classificatory (adj.) Look up classificatory at Dictionary.com
1825, from Latin stem of classify + -ory.
classified (adj.) Look up classified at Dictionary.com
"arranged in classes," 1828, past participle adjective from classify. Meaning "secret" (of government information) is from 1941, American English. Classifieds (n.) "newspaper advertisements arranged by classes," 1913, is short for classified advertisements
classify (v.) Look up classify at Dictionary.com
1782, from French classifier, from classe (see class (n.)) + -fier (see -fy). Related: Classified; classifying.
classism (n.) Look up classism at Dictionary.com
"distinction of class," 1842, from class (n.) + -ism.
classless (adj.) Look up classless at Dictionary.com
1874 in the social sense (1863 in reference to class generally), from class (n.) in the "social order" sense + -less. As "lacking the sophistication of high class," by 1979. Related: Classlessly; classlessness.
classmate (n.) Look up classmate at Dictionary.com
"one of the same class at school or college," 1713, from class (n.) + mate (n.).
classroom (n.) Look up classroom at Dictionary.com
also class-room, 1811, from class (n.) + room (n.).
classy (adj.) Look up classy at Dictionary.com
"pertaining to or characteristic of a (high) class," 1891, from class (n.) + -y (2). Related: Classily; classiness.
clastic (adj.) Look up clastic at Dictionary.com
"consisting of broken pieces," 1875, in geology, from Latinized form of Greek klastos "broken in pieces," from klan, klaein "to break," from PIE *kla-, variant of root *kel- (1) "to strike" (see holt).
clatter (v.) Look up clatter at Dictionary.com
late Old English clatrung "clattering, noise," verbal noun implying an Old English *clatrian, of imitative origin. Compare Middle Dutch klateren, East Frisian klatern, dialectal German klattern. The noun is attested from mid-14c.
Claude Look up Claude at Dictionary.com
masc. proper name, from French form of Claudius.
Claudia Look up Claudia at Dictionary.com
fem. proper name, from Latin Claudius (m.).
claudication (n.) Look up claudication at Dictionary.com
1550s, from Middle French claudication (13c.) or directly from Latin claudicationem (nominative claudicatio) "a limping," noun of action from past participle stem of claudicare "to limp, be lame," from claudus "limping, halting, lame." Related: Claudicant (adj.); claudicate.
Claudius Look up Claudius at Dictionary.com
masc. proper name, from the name of two Roman gentes, perhaps related to claudus "lame," which is of unknown origin. Related: Claudian.
clausal (adj.) Look up clausal at Dictionary.com
1870, from clause + -al (1).
clause (n.) Look up clause at Dictionary.com
c.1200, "a sentence, a brief statement, a short passage," from Old French clause "stipulation" (in a legal document), 12c., from Medieval Latin clausa "conclusion," used in the sense of classical Latin clausula "the end, a closing, termination," also "end of a sentence or a legal argument," from clausa, fem. noun from past participle of claudere "to close, to shut, to conclude" (see close (v.)). Grammatical sense is from c.1300. Legal meaning "distinct condition, stipulation, or proviso" is recorded from late 14c. in English. The sense of "ending" seems to have fallen from the word between Latin and French.
claustral (adj.) Look up claustral at Dictionary.com
"resembling a cloister," early 15c., from Middle French claustral (15c.) and directly from Medieval Latin claustralis "pertaining to a claustrum" (see cloister).
claustration (n.) Look up claustration at Dictionary.com
1863, "act of shutting up in a cloister," as if from a noun of action formed in Latin from Latin claustrare, from claustrum (see cloister).
claustrophilia (n.) Look up claustrophilia at Dictionary.com
"morbid desire to be shut up in a confined space," 1884, from claustro-, abstracted from claustrophobia, + -philia.
claustrophobia (n.) Look up claustrophobia at Dictionary.com
"morbid fear of being shut up in a confined space," coined 1879 (in article by Italian-born, French-naturalized Swiss-English physician Dr. Benjamin Ball (1834-1892)) from Latin claustrum "a bolt, a means of closing; a place shut in, confined place, frontier fortress" (in Medieval Latin "cloister"), past participle of claudere "to close" (see close (v.)) + -phobia "fear."
claustrophobic (adj.) Look up claustrophobic at Dictionary.com
1889, from claustrophobia + -ic. As a noun, "person who has claustrophobia," it is recorded from 1953.
claves (n.) Look up claves at Dictionary.com
pair of hardwood sticks used in making music, 1928, from American Spanish claves (plural), from Spanish clave "keystone," from Latin clavis "key" (see slot (n.2)).
clavichord (n.) Look up clavichord at Dictionary.com
mid-15c., from Medieval Latin clavicordium (15c.), from Latin clavis "a key" (see slot (n.2)) + chorda "a string" (see cord).
clavicle (n.) Look up clavicle at Dictionary.com
"collarbone," 1610s, from Middle French clavicule "collarbone" (16c.), also "small key," from Medieval Latin clavicula "collarbone" (used c.980 in a translation of Avicenna), special use of classical Latin clavicula, literally "small key, bolt," diminutive of clavis "key" (see slot (n.2)); in the anatomical sense a loan-translation of Greek kleis "key, collarbone." So called supposedly from its function as the "fastener" of the shoulder. Related: Clavicular.
clavier (n.) Look up clavier at Dictionary.com
1708, "keyboard," from French clavier, originally "a key-bearer," from Latin clavis "key" (see slot (n.2)). The French word also is the source of German Klavier, Dutch klavier, Danish klaver, etc. The German word is the direct source of the name of the musical instrument, a sense attested from 1845 in English.
claviger (n.) Look up claviger at Dictionary.com
"one who carries a club," c.1600, from Latin claviger (an epithet of Hercules), from clava "club, knotty branch" + stem of gerere "to bear" (see gest).
claw (n.) Look up claw at Dictionary.com
Old English clawu, earlier clea, "claw, talon, iron hook," from Proto-Germanic *klawo (cognates: Old Frisian klawe "claw, hoe," Middle Dutch klouwe, Dutch klauw, Old High German klawa, German Klaue "claw").

Claw-foot in reference to furniture is from 1823; claw-and-ball attested from 1893. Claw-hammer attested from 1769.
claw (v.) Look up claw at Dictionary.com
Old English clawian "to scratch, claw," from the same root as claw (n.). Related: Clawed; clawing. Compare Dutch klaauwen, Old High German klawan, German klauen. To claw back"regain by great effort" is from 1953; as a noun, an act of this, from 1969.
clay (n.) Look up clay at Dictionary.com
Old English clæg "stiff, sticky earth; clay," from Proto-Germanic *klaijaz (cognates: Old High German kliwa "bran," German Kleie, Old Frisian klai "clay," Old Saxon klei, Middle Dutch clei, Danish klæg "clay;" also Old English clæman, Old Norse kleima, Old High German kleiman "to cover with clay"), from PIE root *glei- "clay" (cognates: Greek gloios "sticky matter;" Latin gluten "glue;" Old Church Slavonic glina "clay," glenu "slime, mucus;" Old Irish glenim "I cleave, adhere").

in Scripture, the stuff from which the body of the first man was formed; hence "human body" (especially when dead). Clay pigeon is from 1888. Feet of clay "fundamental weakness" is from Dan. ii:33.
clayey (adj.) Look up clayey at Dictionary.com
Old English clæig, from contracted compound of clæg (see clay) + -ig (see -y (2)).
claymore (n.) Look up claymore at Dictionary.com
1749, "two-edged broadsword of ancient Scottish Highlanders," from Gaelic claidheamh mor "great sword," from claidheb "sword" (compare Welsh cleddyf), possibly from PIE root *kel- (1) "to strike" (see holt) + mor "great" (compare Welsh mawr; see more). An antiquarian word made familiar again by Scott's novels; modern military application to pellet-scattering anti-personnel mine is first attested 1962.
clean (adj.) Look up clean at Dictionary.com
Old English clæne "free from dirt or filth; pure, chaste, innocent; open, in the open," of beasts, "ritually safe to eat," from West Germanic *klainoz "clear, pure" (cognates: Old Saxon kleni "dainty, delicate," Old Frisian klene "small," Old High German kleini "delicate, fine, small," German klein "small;" English preserves the original Germanic sense), from PIE root *gel- "bright, gleaming" (cognates: Greek glene "eyeball," Old Irish gel "bright").

"Largely replaced by clear, pure in the higher senses" [Weekley], but as a verb (mid-15c.) it has largely usurped what once belonged to cleanse. Meaning "whole, entire" is from c.1300 (clean sweep in the figurative sense is from 1821). Sense of "innocent" is from c.1300; that of "not lewd" is from 1867; that of "not carrying anything forbidden" is from 1938; that of "free of drug addiction" is from 1950s. To come clean "confess" is from 1919, American English.
clean (v.) Look up clean at Dictionary.com
mid-15c., "make clean," from clean (adj.). Related: Cleaned; cleaning. From clean out "clean by emptying" comes sense of "to leave bare" (1844); cleaned-out "left penniless by losses" is from 1812.
clean (adv.) Look up clean at Dictionary.com
Old English clæne "dirtlessly," also "clearly, fully, entirely;" see clean (adj.). Compare similar use of German rein "clean."
clean-cut (adj.) Look up clean-cut at Dictionary.com
"precise," 1829 (of turf), from clean (adv.) + past participle of cut (v.).
clean-living (adj.) Look up clean-living at Dictionary.com
1920, from clean (adv.) + live (v.).
clean-up (n.) Look up clean-up at Dictionary.com
also cleanup, 1856, "act of cleaning up," from clean + up. Meaning "a profit" is recorded from 1878. Verbal phrase clean up "make a large profit" is from 1929. The adjective, in the baseball sense, is recorded by 1910.
cleaner (n.) Look up cleaner at Dictionary.com
mid-15c., agent noun from clean (v.). Meaning "shop that cleans clothes" is from 1873. To take (someone) to the cleaners "get all of (someone's) money" is from 1921.
cleanliness (n.) Look up cleanliness at Dictionary.com
early 15c., from cleanly + -ness.
Cleanliness is indeed next to godliness. [John Wesley, Sermon "On Dress," c.1791]
cleanly (adj.) Look up cleanly at Dictionary.com
Old English clænlic "morally pure, innocent," from clæne (see clean (adj.)). Of persons, "habitually clean," from c.1500.
cleanly (adv.) Look up cleanly at Dictionary.com
Old English clænlice; see clean (adj.) + -ly (2).