decimal (adj.) Look up decimal at Dictionary.com
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.
decimate (v.) Look up decimate at Dictionary.com
c.1600, in reference to the practice of punishing mutinous military units by capital execution of one in every 10, by lot; from Latin decimatus, past participle of decimare (see decimation). Killing one in ten, chosen by lots, from a rebellious city or a mutinous army was a common punishment in classical times. The word has been used (incorrectly, to the irritation of pedants) since 1660s for "destroy a large portion of." Related: Decimated; decimating.
decimation (n.) Look up decimation at Dictionary.com
mid-15c., from Late Latin decimationem (nominative decimatio), noun of action from past participle stem of Latin decimare "the removal or destruction of one-tenth," from decem "ten" (see ten). Earliest sense in English was of a tithe; punishment sense is from 1580s; transferred sense of "much destruction, severe loss" recorded from 1680s.
decimeter (n.) Look up decimeter at Dictionary.com
1809, from deci- + meter (n.2).
decipher (v.) Look up decipher at Dictionary.com
1520s, from de- + cipher. Perhaps in part a loan-translation from Middle French déchiffrer. Related: Deciphered; deciphering.
decision (n.) Look up decision at Dictionary.com
mid-15c., from Middle French décision (14c.), from Latin decisionem (nominative decisio) "a decision, settlement, agreement," noun of action from past participle stem of decidere (see decide). Decision making (adjective, also decision-making) is recorded from 1953.
decisive (adj.) Look up decisive at Dictionary.com
1610s, from Medieval Latin decisivus, from Latin decis-, past participle stem of decidere (see decide). Related: Decisively; decisiveness.
deck (n.) Look up deck at Dictionary.com
"covering over part of a ship," mid-15c., perhaps a shortening of Middle Low German verdeck (or a related North Sea Germanic word), a nautical word, from ver- "fore" + decken "to cover, put under roof," from Proto-Germanic *thackjam (related to thatch, q.v.).

Sense extended early in English from "covering" to "platform of a ship." "Pack of cards" is 1590s, perhaps because they were stacked like decks of a ship. Deck chair (1884) so called because they were used on ocean liners. Tape deck (1949) is in reference to the flat surface of old reel-to-reel tape recorders.
deck (v.2) Look up deck at Dictionary.com
"knock down," c.1953, probably from deck (n.) on the notion of laying someone out on the deck. Related: Decked; decking.
deck (v.1) Look up deck at Dictionary.com
"adorn" (as in deck the halls), early 15c., from Middle Dutch dekken "to cover," from the same Germanic root as deck (n.). Meaning "to cover" is from 1510s in English. Replaced Old English þeccan. Related: Decked; decking.
deckhand (n.) Look up deckhand at Dictionary.com
1844, American English, from deck (n.) + hand (n.).
deckle (n.) Look up deckle at Dictionary.com
1810, in paper-making, from German deckel "lid, little cover," diminutive of decke "cover" (see deck (n.)).
declaim (v.) Look up declaim at Dictionary.com
late 14c., from Middle French déclamer and directly from Latin declamare "to practice public speaking, to bluster," from de- intensive prefix + clamare "to cry, shout" (see claim (v.)). At first in English spelled declame, but altered under influence of claim. Related: Declaimed; declaiming.
declamation (n.) Look up declamation at Dictionary.com
late 14c., from Latin declamationem (nominative declamatio), noun of action from past participle stem of declamare (see declaim).
declamatory (adj.) Look up declamatory at Dictionary.com
1580s, from Latin declamatorius "pertaining to the practice of speaking," from declamatus, past participle of declamare (see declaim).
declarant (n.) Look up declarant at Dictionary.com
1680s, from French déclarant, from Latin declarantem (nominative declarans), present participle of declarare (see declare).
declaration (n.) Look up declaration at Dictionary.com
mid-14c., "action of stating," from Old French declaration, from Latin declarationem (nominative declaratio), noun of action from past participle stem of declarare (see declare). Meaning "proclamation, public statement" is from 1650s. Declaration of independence is recorded from 1776 (the one by the British American colonies seems to be the first so called; though the phrase is not in the document itself, it was titled that from the first in the press).
declarative (adj.) Look up declarative at Dictionary.com
mid-15c., from French déclaratif and directly from Late Latin declarativus, from past participle stem of Latin declarare (see declare).
declaratory (adj.) Look up declaratory at Dictionary.com
mid-15c., from Medieval Latin declaratorius, from Latin declarator, from declarare (see declare).
declare (v.) Look up declare at Dictionary.com
early 14c., from Old French declarer "explain, elucidate," or directly from Latin declarare "make clear, reveal, disclose, announce," from de- intensive prefix (see de-) + clarare "clarify," from clarus "clear" (see clear (adj.)). Related: Declared; declaring.
declasse (adj.) Look up declasse at Dictionary.com
1887, from French déclassé, past participle of déclasser "to cause to lose class," from de-, privative prefix (see de-) + classer "to class" (see class).
declassify (v.) Look up declassify at Dictionary.com
1865, originally a term in logic; with reference to state secrets, 1946; from de- + classify. Related: Declassification; declassified; declassifying.
declension (n.) Look up declension at Dictionary.com
mid-15c., ultimately from Latin declinationem (nominative declinatio), noun of action from past participle stem of declinare (see decline (v.)); perhaps via French; "the form is irregular, and its history obscure" [OED].
declination (n.) Look up declination at Dictionary.com
late 14c. as a term in astronomy, from Old French declinacion (Modern French déclinaison), from Latin declinationem (nominative declinatio), noun of action from past participle stem of declinare (see decline (v.)). It took on various other senses 15c.-17c., most now obsolete.
decline (v.) Look up decline at Dictionary.com
late 14c., "to turn aside, deviate," from Old French decliner "to sink, decline, degenerate, turn aside," from Latin declinare "to lower, avoid, deviate, to bend from, inflect," from de- "from" (see de-) + clinare "to bend," from PIE *klei-n-, suffixed form of *klei- "to lean" (see lean (v.)). Sense has been altered since c.1400 by interpretation of de- as "downward." Meaning "not to consent, politely refuse," is from 1630s. Related: Declined; declining.
decline (n.) Look up decline at Dictionary.com
early 14c., "deterioration, degeneration," from Old French declin (see decline (v.)).
declivity (n.) Look up declivity at Dictionary.com
1610s, from French déclivité, from Latin declivitatem (nominative declivitas) "a slope, declivity," from declivis "a sloping downward," from de- "down" (see de-) + clivus "a slope," from PIE *klei-wo-, suffixed form of *klei "to lean" (see lean (v.)).
decoct (v.) Look up decoct at Dictionary.com
early 15c., from Latin decoctus, past participle of decoquere (see decoction). Related: Decocted; decocting.
decoction (n.) Look up decoction at Dictionary.com
late 14c., from French décoction (13c.) or directly from Latin decoctionem (nominative decoctio) "a boiling down," noun of action from past participle stem of decoquere "to boil down," from de- "down" (see de-) + coquere "to cook" (see cook (n.)).
decode (v.) Look up decode at Dictionary.com
1896, from de- + code. Related: Decoded; decoding.
decolletage (n.) Look up decolletage at Dictionary.com
1894 (from 1883 as a French word in English), from French décolletage, from décolleté "low-necked" (see decollete).
decollete (adj.) Look up decollete at Dictionary.com
1831, from French décolleté, past participle of décolleter "to bare the neck and shoulders," from de- (see de-) + collet "collar of a dress," diminutive of col (Latin collum) "neck" (see collar (n.)). Not to be confused with decollate (v.), which means "to behead."
decolonization (n.) Look up decolonization at Dictionary.com
1853 in political sense, American English, from de- + colonization. Earlier as a medical term.
decommission (v.) Look up decommission at Dictionary.com
1922, originally with reference to warships, from de- + commission (v.). Related: Decommissioned; decommissioning.
decompensate (v.) Look up decompensate at Dictionary.com
1912, probably a back-formation from decompensation. Related: Decompensated; decompensating.
decompensation (n.) Look up decompensation at Dictionary.com
1900, from de- + compensation.
decompose (v.) Look up decompose at Dictionary.com
1750s, "to separate into components," from de- "opposite of" + compose. Sense of "putrefy" is first recorded 1777. Related: Decomposed; decomposing.
decomposer (n.) Look up decomposer at Dictionary.com
1833, "a decomposing agent," agent noun from decompose.
decomposition (n.) Look up decomposition at Dictionary.com
1762, from de- + composition. An earlier word in the same form meant "further compounding of already composite things" (1650s).
decompress (v.) Look up decompress at Dictionary.com
1905, from de- + compress (v.). Related: Decompressed; decompressing.
decompression (n.) Look up decompression at Dictionary.com
1905, from de- + compression.
decongestant (n.) Look up decongestant at Dictionary.com
1950, from de- + congestant (see congest).
deconstruct (v.) Look up deconstruct at Dictionary.com
1973, back-formation from deconstruction. Related: Deconstructed; deconstructing.
deconstruction (n.) Look up deconstruction at Dictionary.com
1973, as a strategy of critical analysis, in translations from French of the works of philosopher Jacques Derrida (1930-2004). The word was used in English in a literal sense from 1865 of building and architecture, and in late 1860s sometimes as an ironic variant of Reconstruction in the U.S. political sense.
decontaminate (v.) Look up decontaminate at Dictionary.com
1936, from de- + contaminate. Originally in reference to poison gas. Related: Decontaminated; decontaminating.
decor (n.) Look up decor at Dictionary.com
1897, from French décor (18c.), back-formation from décorer "to decorate" (14c.), from Latin decorare (see decorate). It thus duplicates Latin decor "beauty, elegance, charm, grace, ornament." Originally a theater term in English; general use is since 1926.
decorate (v.) Look up decorate at Dictionary.com
early 15c., from Latin decoratus, past participle of decorare "to decorate, adorn, embellish, beautify," from decus (genitive decoris) "an ornament," from PIE root *dek- "to receive, be suitable" (see decent). Related: Decorated; decorating.
decoration (n.) Look up decoration at Dictionary.com
early 15c., "action of decorating, beautification," from Late Latin decorationem (nominative decoratio), noun of action from past participle stem of decorare (see decorate). Meaning "that which decorates" is from 1670s. As "a badge or medal worn as a mark of honor," it is attested from 1816 (often in plural, decorations).
decorative (adj.) Look up decorative at Dictionary.com
early 15c., from Middle French decoratif, from decorat-, past participle stem of Latin decorare (see decorate).
decorator (n.) Look up decorator at Dictionary.com
1755, agent noun in Latin form from decorate.