expectancy (n.)
1590s, from Latin expectantia (see expectant) + -ancy.
expectant (adj.)
late 14c., from Old French expectant or directly from Latin expectantem/exspectantem (nominative expectans/exspectans), present participle of expectare/exspectare (see expect). Related: Expectantly. As a noun, from 1620s.
expectation (n.)
1530s, from Middle French expectation (14c.) or directly from Latin expectationem/exspectationem (nominative expectatio/exspectatio) "anticipation, an awaiting," noun of action from past participle stem of expectare/exspectare (see expect). Related: Expectations.
expectorant (n.)
1782, from Latin expectorantem (nominative expectorans), present participle of expectorare (see expectorate). From 1811 as an adjective.
expectorate (v.)
c.1600, "to clear out the chest or lungs," from Latin expectoratus, past participle of expectorare "scorn, expel from the mind," literally "make a clean breast," from ex- "out" (see ex-) + pectus (genitive pectoris) "breast" (see pectoral (adj.)). Use as a euphemism for "spit" is first recorded 1827. Original sense in expectorant. Related: Expectorated; expectorating.
expectoration (n.)
1670s, noun of action from expectorate.
expediate (v.)
a 17c. error for expedite that has gotten into the dictionaries.
expedience (n.)
mid-15c., "advantage, benefit," from Old French expedience, from Late Latin expedientia, from expedientem (see expedient). Related: Expediency (1610s).
expedient (adj.)
late 14c., "advantageous, fit, proper," from Old French expedient (14c.) or directly from Latin expedientem (nominative expediens) "beneficial," present participle of expedire "make fit or ready, prepare" (see expedite). The noun meaning "a device adopted in an exigency, a resource" is from 1650s. Related: Expediential; expedientially (both 19c.)
expediently (adv.)
late 14c., from expedient (adj.) + -ly (2).
expedite (v.)
late 15c. (implied in past participle expedit), from Latin expeditus, past participle of expedire "extricate, disengage, liberate; procure, make ready, make fit, prepare," literally "free the feet from fetters," hence "liberate from difficulties," from ex- "out" (see ex-) + *pedis "fetter, chain for the feet," related to pes (genitive pedis) "foot" (see foot (n.)). Compare Greek pede "fetter." Related: Expedited; expediting.
expedition (n.)
early 15c., "military campaign; the act of rapidly setting forth," from Middle French expédition (13c.) and directly from Latin expeditionem (nominative expeditio), noun of action from past participle stem of expedire (see expedite). Meaning "journey for some purpose" is from 1590s. Sense by 1690s also included the body of persons on such a journey. Related: Expeditionary.
expeditious (adj.)
late 15c., expedycius "useful, fitting," from Latin expeditus "disengaged, ready, prompt," past participle of expidere (see expedite). Meaning "speedy" is from 1590s. Related: Expeditiously; expeditiousness.
expel (v.)
late 14c., from Latin expellere "drive out," from ex- "out" (see ex-) + pellere "to drive" (see pulse (n.1)). Meaning "to eject from a school" is first recorded 1640s. Related: Expelled; expelling.
expellee (n.)
1888, from expel + -ee.
expend (v.)
early 15c., from Latin expendere "pay out, weigh out money," from ex- "out" (see ex-) + pendere "to pay, weigh" (see pendant). Related: Expended; expending.
expendable (adj.)
1805, from expend + -able.
expenditure (n.)
1769, from Medieval Latin expenditus, irregular past participle of expendere (see expend) + -ure. Related: Expenditures.
expense (n.)
late 14c., from Anglo-French expense, Old French espense "money provided for expenses," from Late Latin expensa "disbursement, outlay, expense," noun use of neuter plural past participle of Latin expendere "to weigh out money, to pay down" (see expend).

Latin spensa also yielded Medieval Latin spe(n)sa, whose sense specialized to "outlay for provisions," then "provisions, food," which was borrowed into Old High German as spisa and is the root of German Speise "food," now mostly meaning prepared food, and speisen "to eat."
expense (v.)
1909, from expense (n.). Related: Expensed; expensing.
expenses (n.)
"charges incurred in the discharge of duty," late 14c. See expense (n.).
expensive (adj.)
1620s, "given to profuse expenditure," from expense (n.) + -ive. Meaning "costly" is from 1630s. Earlier was expenseful (c.1600). Expenseless was in use mid-17c.-18c., but there seems now nothing notable to which it applies, and the dictionaries label it "obsolete."
experience (n.)
late 14c., "observation as the source of knowledge; actual observation; an event which has affected one," from Old French esperience (13c.) "experiment, proof, experience," from Latin experientia "knowledge gained by repeated trials," from experientem (nominative experiens), present participle of experiri "to try, test," from ex- "out of" (see ex-) + peritus "experienced, tested," from PIE root *per- "to lead, pass over" (see peril). Meaning "state of having done something and gotten handy at it" is from late 15c.
experience (v.)
1530s, "to test, try;" see experience (n.). Sense of "feel, undergo" first recorded 1580s. Related: Experienced; experiences; experiencing.
experienced (adj.)
"having experience; skillful through expereince," 1570s, past participle adjective from experience (v.).
experiential (adj.)
1640s (implied in experientially), from Latin experientia (see experience (n.)) + -al (1).
experiment (n.)
mid-14c., from Old French esperment "practical knowledge, cunning, enchantment; trial, proof, example, lesson," from Latin experimentum "a trial, test, proof, experiment," noun of action from experiri "to test, try" (see experience (n.)).
experiment (v.)
late 15c., from experiment (n.). Related: Experimented; experimenting.
experimental (adj.)
mid 15c., "having experience," from experiment (n.) + -al (1). Meaning "based on experience" is from 1560s. Meaning "for the sake of experiment" is from 1792 (as in Experimental farm).
experimentation (n.)
1670s; see experiment (v.) + -ation.
expert (adj.)
late 14c., from Old French expert and directly from Latin expertus, past participle of experiri "to try, test" (see experience). The noun sense of "person wise through experience" existed 15c., reappeared 1825. Related: Expertly.
expertise (n.)
1868, from French expertise (16c.) "expert appraisal, expert's report," from expert (see expert). Earlier in same sense was expertness (c.1600).
experto crede
Latin ("Aeneid," xi.283), "take it from one who knows;" from dative singular of expertus (see expert (adj.)) + imperative singular of credere (see credo).
expiate (v.)
c.1600 (OED entry has a typographical error in the earliest date), from Latin expiatus, past participle of expiare "to make amends, atone for" (see expiation). Related: Expiable (1560s); expiated; expiating.
expiation (n.)
early 15c., via Middle French expiation or directly from Latin expiationem (nominative expiatio) "satisfaction, atonement," noun of action from past participle stem of expiare "make amends," from ex- "completely" (see ex-) + piare "propitiate, appease," from pius "faithful, loyal, devout" (see pious).
The sacrifice of expiation is that which tendeth to appease the wrath of God. [Thomas Norton, translation of Calvin's "Institutes of Christian Religion," 1561]
expiatory (adj.)
1540s, from Latin expiatorius, from expiat-, past participle stem of expiare (see expiation).
expiration (n.)
early 15c., "vapor, breath," from Middle French expiration, from Latin expirationem/exspirationem (nominative expiratio/exspiratio), noun of action from past participle stem of expirare/exspirare (see expire). Meaning "termination, end, close" is from 1560s.
expire (v.)
c.1400, "to die," from Middle French expirer (12c.) "expire, elapse," from Latin expirare/exspirare "breathe out, breathe one's last, die," from ex- "out" (see ex-) + spirare "to breathe" (see spirit (n.)). "Die" is the older sense in English; that of "breathe out" is first attested 1580s. Of laws, patents, treaties, etc., mid-15c. Related: Expired; expiring.
expiry (n.)
"close, termination," 1752, from expire + -y (4). Meaning "dying, death" is from 1790.
explain (v.)
early 15c., from Latin explanare "to make level, smooth out;" also "to explain, make clear" (see explanation).

Originally explane, spelling altered by influence of plain. Also see plane (v.2). In 17c., occasionally used more literally, of the unfolding of material things: Evelyn has buds that "explain into leaves" ["Sylva, or, A discourse of forest-trees, and the propagation of timber in His Majesties dominions," 1664]. Related: Explained; explaining; explains.
explanation (n.)
late 14c., from Latin explanationem (nominative explanatio), noun of action from past participle stem of explanare "to make plain or clear, explain," literally "make level, flatten," from ex- "out" (see ex-) + planus "flat" (see plane (n.1)).
explanatory (adj.)
1610s, from or modeled on Late Latin explanatorius "having to do with an explanation," from Latin explanat-, past participle stem of explanare (see explanation).
expletive (n.)
1610s, originally "a word or phrase serving to fill out a sentence or metrical line," from Middle French explétif (15c.) and directly from Late Latin expletivus "serving to fill out," from explet-, past participle stem of Latin explere "fill out," from ex- "out" (see ex-) + plere "to fill" (see pleio-).

Sense of "exclamation," often in the form of a cuss word, first recorded 1815 in Sir Walter Scott, popularized by edited transcripts of Watergate tapes (mid-1970s), in which expletive deleted replaced President Nixon's salty expressions. As an adjective, from 1660s.
expletive (adj.)
mid-15c., from Latin expletivus (see expletive (n.)).
explicable (adj.)
1550s, from or on model of Latin explicabilis "capable of being unraveled, that may be explained," from explicare (see explicit). Middle English had a verb expliken "explain, interpret" (mid-15c.).
explicate (v.)
1530s, from Latin explicatus, past participle of explicare "unfold, unravel, explain" (see explicit). Related: Explicated; explicating.
explication (n.)
1520s, from Middle French explication, from Latin explicationem (nominative explicatio), noun of action from past participle stem of explicare (see explicit).
explicative (adj.)
1640s, "having the function of explaining," from Latin explicativus, from past participle stem of explicare (see explicit). As a noun, from 1775.
explicit (adj.)
c.1600, from French explicite, from Latin explicitus "unobstructed," variant past participle of explicare "unfold, unravel, explain," from ex- "out" (see ex-) + plicare "to fold" (see ply (v.1)).

"Explicitus" was written at the end of medieval books, originally short for explicitus est liber "the book is unrolled." As a euphemism for "pornographic" it dates from 1971.
explicitly (adv.)
1630s, from explicit + -ly (2). Opposed to implicitly.