Online Etymology Dictionary

debt (n.): late 13c., dette, from Old French dete, from Latin debitum "thing owed," neuter past participle of debere "to owe," originally, "keep something away from someone," from de- "away" (see de-) + habere "to have" (see habit). Restored spelling after c.1400.
debtor (n.): early 13c., dettur, dettour, from Old French detour, from Latin debitor "a debter," from past participle stem of debere; see debt. The -b- was restored in later French, and in English c.1560-c.1660. The KJV has detter three times, debter three times, debtor twice and debtour once.
debug (v.): 1945, of machine systems, from de- + bug (n.) "glitch, defect in a machine." Meaning "to remove a concealed microphone" is from 1964. Related: Debugged; debugging.
debunk (v.): 1923, from de- + bunk (n.2); first used by U.S. novelist William Woodward (1874-1950), the notion being "to take the bunk out of things." Related: Debunked; debunking.
debut (n.): 1751, from French début "first appearance," a figurative use from débuter "make the first stroke at billiards," also "to lead off at bowls" (a game akin to bowling), 16c., from but "mark, goal," from Old French but "end" (see butt (n.3)). The verb is first attested 1830.
Début can only be pronounced as French, and should not be used by anyone who shrinks from the necessary effort. [Fowler]
debutant (n.): 1824, "male performer or speaker making his first public appearance," from French, noun use of present participle of débuter "to make the first strike" (in billiards, etc.), from debut (see debut).
debutante (n.): 1801, "female stage actress making her first public performance," from fem. of French debutant (q.v.). In reference to a young woman making her first appearance in society, from 1817.
deca-: before a vowel, dec-, word-forming element meaning "ten," from Latinized comb. form of Greek deka "ten" (see ten). In the metric system, "multiplied by ten;" while deci- means "divided by ten."
decade (n.): mid-15c., "ten parts" (of anything; originally in reference to the books of Livy), from Middle French décade (14c.), from Late Latin decadem (nominative decas), from Greek dekas (genitive dekados) "group of ten," from deka "ten" (see ten). Meaning "period of ten years" is 1590s in English.
decadence (n.): 1540s, from Middle French décadence (early 15c.), from Medieval Latin decadentia "decay," from decadentem (nominative decadens) "decaying," present participle of decadere "to decay," from Latin de- "apart, down" (see de-) + cadere "to fall" (see case (n.1)). Used of periods in art since 1852, on French model.
decadent (adj.): "in a state of decline or decay (from a former condition of excellence)," 1837, from French décadent, back-formation from décadence (see decadence). In reference to literary (later, other artistic) schools that believed, or affected to believe, they lived in an age of artistic decadence, 1885 in French, 1888 in English. Usually in a bad sense, e.g.:
"Bread, supposedly the staff of life, has become one of our most decadent foods -- doughy, gummy, and without the aroma, flavor, texture, taste and appearance that is typical of good bread." ["College and University Business" 1960]
Beckoning sense of "desirable and satisfying to self-indulgence" begins c.1970 in commercial publications in reference to desserts.
decaffeinate (v.): 1909 (implied in decaffeinated), from de- + caffeine + -ate (2).
decagon (n.): early 17c., from Modern Latin decagonum, from Greek dekagonon, from deka "ten" (see ten) + gonia "corner, angle" (see knee (n.)).
decal (n.): by 1909, shortening of decalcomania, from French décalcomanie, from décalquer (18c.) "transferring of a tracing from specially prepared paper to glass, porcelain, etc." (in vogue in France 1840s, England 1862-64), from de- "off" + calquer "to press," from Italian calcare, from Latin calcare "to tread on, press."
Time was when there were only printers employed in making the sheets that were stuck on the ware, giving the old-time term of "plain print." This form of decoration was succeeded a few years ago by the decalcomania or "decal." This "decal" is an imported sheet, lithographed, and the little sprigs, flowers and scenes are cut out and stuck on the ware. ["Brick, the Leading Clay Journal," April 1909]
Decalogue (n.): "Ten Commandments," late 14c., from Middle French decalogue, from Latin decalogus, from Greek, from the phrase hoi deka logoi used to translate "Ten Commandments" in Septuagint.
Decameron (n.): c.1600, from Italian Decamerone, name of Boccaccio's 14c. collection of 100 tales supposedly told over 10 days, from Greek deka "ten" (see ten) + hemera "day" (see ephemera).
decamp (v.): 1670s, from French décamper (17c.), earlier descamper, from des- (see dis-) + camper (see camp (n.)). Non-military use is from 1751. Related: Decamped; decamping.
decant (v.): 1630s, "pour off the clear liquid from a solution by gently tipping the vessel," originally an alchemical term, from French décanter, perhaps from Medieval Latin decanthare "to pour from the edge of a vessel," from de- + Medieval Latin canthus "corner, lip of a jug," from Latin cantus, canthus "iron rim around a carriage wheel." Related: Decanted; decanting.
decanter (n.): vessel for decanting liquors, 1715, agent noun from decant.
decapitate (v.): 1610s, from French décapiter (14c.), from Late Latin decapitatus past participle of decapitare, from Latin de- "off" (see de-) + caput (genitive capitis) "head" (see capitulum). Related: Decapitated; decapitating.
decapitation (n.): 1640s, from French décapitation, from Medieval Latin decapitationem (nominative decapitatio), noun of action from past participle stem of Late Latin decapitare (see decapitate).
decapod (n.): 1835 as a type of crustacean having 10 legs, from French décapode (1806), from Modern Latin Decapoda (animalia), from Greek dekapoda, neuter plural of dekapous "ten-footed" (see ten + foot (n.)). From 1888 as a type of locomotive.
decathlon (n.): 1912, from deca "ten" (see ten) + Greek athlon "contest, prize," of uncertain origin. A modern Olympic event consisting of 10 challenges.
decay (v.): late 15c., "to decrease," from Anglo-French decair, Old North French decair (Old French decheoir, 12c., Modern French déchoir) "to fall, set (of the sun), weaken, decline, decay," from Vulgar Latin *decadere "to fall off," from de- (see de-) + Latin cadere "to fall" (see case (n.1)). Meaning "decline, deteriorate" is c.1500; that of "to decompose, rot" is from 1570s. Related: Decayed; decaying.
decay (n.): mid-15c., "deterioration, decline in value," from decay (v.). Meaning "gradual decrease in radioactivity" is from 1897.
decease (n.): "death," early 14c., from Old French deces (12c., Modern French décès) "decease, death," from Latin decessus "death" (euphemism for mors), also "a retirement, a departure," from decess-, past participle stem of decedere "die, depart, withdraw," literally "to go down," from de- "away" (see de-) + cedere "go" (see cede). Still used with a tinge of euphemism.
decease (v.): "to die," early 15c., from decease (n.). Related: Deceased; deceasing
deceased (adj.): late 15c., past participle adjective from decease (v.). As a verbal noun meaning "dead person, those who are dead," from early 17c.
decedent (n.): 1730, "dead person," mostly as a term in law, from Latin decedentem, present participle of decedere "to die, to depart" (see decease (n.)).
deceit (n.): c.1300, from Old French deceite, fem. past participle of deceveir (see deceive).
Deceit is a shorter and more energetic word for deceitfulness, indicating the quality; it is also, but more rarely, used to express the act or manner of deceiving. The reverse is true of deception, which is properly the act or course by which one deceives, and not properly the quality; it may express the state of being deceived. Fraud is an act or series of acts of deceit by which one attempts to benefit himself at the expense of others. It is generally a breaking of the law; the others are not. [entry for "deceit" in "The Century Dictionary and Cyclopedia," 1902]
deceitful (adj.): mid-15c., from deceit + -ful. Related: Deceitfully; deceitfulness.
deceive (v.): c.1300, from Old French decevoir (12c., Modern French décevoir) "to deceive," from Latin decipere "to ensnare, take in, beguile, cheat," from de- "from" or pejorative + capere "to take" (see capable). Related: Deceived; deceiver; deceiving.
decelerate (v.): 1899, back-formation from deceleration. Related: Decelerated; decelerating.
deceleration (n.): 1894, originally in railroading, coined from de- "do the opposite of" (see de-) + (ac)celeration.
Verily "deceleration" is a word which could only be coined by the Great Western. ["Engineering," Feb. 2, 1894]
December (n.): c.1000, from Old French decembre, from Latin December, from decem "ten" (see ten); tenth month of the old Roman calendar, which began with March.

The -ber in four Latin month names is probably from -bris, an adjectival suffix. Tucker thinks that the first five months were named for their positions in the agricultural cycle, and "after the gathering in of the crops, the months were merely numbered."
If the word contains an element related to mensis, we must assume a *decemo-membris (from *-mensris). October must then be by analogy from a false division Sep-tem-ber &c. Perhaps, however, from *de-cem(o)-mr-is, i.e. "forming the tenth part or division," from *mer- ..., while October = *octuo-mr-is. [T.G. Tucker, "Etymological Dictionary of Latin"]
decency (n.): 1560s, "appropriateness," from Latin decentia "comeliness, decency," from decentem "becoming, fitting" (see decent). Meaning "modesty" (i.e. "appropriateness to standards of society") is from 1630s.
decennial (adj.): 1680s, from Latin decennium, from decennis "of 10 years," from decem "ten" (see ten) + annus "year" (see annual). For vowel change, see biennial.
decent (adj.): 1530s, "proper to one's station or rank," also "tasteful," from Middle French décent, or directly from Latin decentem (nominative decens) "becoming, seemly, fitting, proper," present participle of decere "to be fitting or suitable," from PIE *deke-, from root *dek- "to take, accept, to receive, greet, be suitable" (cf. Greek dokein "to appear, seem, think," dekhesthai "to accept;" Sanskrit daśasyati "shows honor, is gracious," dacati "makes offerings, bestows;" Latin docere "to teach," decus "grace, ornament"). Meaning "kind, pleasant" is from 1902. Are you decent? (1949) was originally backstage theater jargon for "are you dressed."
decentralization (n.): 1839, from de- + centralization.
decentralize (v.): 1840 (implied in decentralized), probably a back-formation from decentralization. Related: Decentralizing.
deception (n.): early 15c., from Middle French déception (13c., decepcion) or directly from Late Latin deceptionem (nominative deceptio) "a deceiving," from Latin decept-, past participle stem of decipere (see deceive).
deceptive (adj.): 1610s, from French deceptif (late 14c.), from Medieval Latin deceptivus, from decept-, past participle stem of Latin decipere (see deceive). Earlier in this sense was deceptious (c.1600), from French deceptieux, from Medieval Latin deceptiosus, from deceptionem. Related: Deceptively; deceptiveness.
decession (n.): c.1600, from Latin decessionem, noun of action from past participle stem of decedere "to go down, depart" (see decease (n.)).
deci-: in the metric system, word-forming element denoting weights of one-tenth of the standard unit of measure, 1801, from French deci-, taken arbitrarily from Latin decimus "tenth," from decem "ten" (see ten).
decibel (n.): 1928, from deci- + bel (n.).
decide (v.): late 14c., "to settle a dispute," from Old French decider, from Latin decidere "to decide, determine," literally "to cut off," from de- "off" (see de-) + caedere "to cut" (see -cide). For Latin vowel change, see acquisition. Sense is of resolving difficulties "at a stroke." Meaning "to make up one's mind" is attested from 1830. Related: Decided; deciding.
decided (adj.): "resolute," 1790, past participle adjective from decide. A decided victory is one whose reality is not in doubt; a decisive one goes far toward settling some issue. Related: Decidedly.
deciduous (adj.): 1680s, from Latin deciduus "that which falls off," from decidere "to fall off," from de- "down" (see de-) + cadere "to fall" (see case (n.1)). Originally with reference to leaves, petals, teeth, etc.; specific sense of "trees whose leaves fall off" (opposed to evergreen) is from 1778.
decile (adj.): 1670s in astrology; 1882 in statistics; from French décile or Medieval Latin *decilis, from Latin decem "ten" (see ten) on the model of quintilis, sextilis.
decimal (adj.): c.1600, from Medeival Latin decimalis "of tithes or tenths," from Latin decimus "tenth," from decem "ten" (see ten). Applied to Arabic notation before modern sense of "decimal fractions" emerged. As a noun from 1640s.