"twelfth and last (by modern reckoning) month of the calendar, the month of the winter solstice," late Old English, from Old French decembre, from Latin December, from decem "ten" (from PIE root *dekm- "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"]
Decembrist, in Russian history in reference to the insurrection against Nicholas I in December 1825, is by 1868 in English, translating Russian dekabrist, from dekabr' "December."
1560s, "appropriateness, state or quality of being fit or suitable," from Latin decentia "comeliness, decency," from decentem "becoming, fitting," present participle of decere "to be fitting or suitable," from PIE *deke-, from root *dek- "to take, accept." Meaning "modesty, freedom from ribaldry or obscenity" (i.e. "appropriateness to standards of society") is from 1630s.
1530s, "proper to one's station or rank," also "tasteful, proper with regard to modesty or social standards," from 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"). Related: Decently.
Meaning "kind, pleasant" is from 1902. Meaning "moderate, respectable, good enough" is by 1711. Are you decent? "are you dressed?" (1949) was originally backstage theater jargon.
"act or principle of removing local or special functions of government from immediate control of central authority," 1839, from de- + centralization. Decentralisation is attested by 1835 in German, in reference to France, but the word does not seem to appear in French before the earliest English dates.
"distribute or take away from a center," 1840 (implied in decentralized), perhaps a back-formation from decentralization. Related: Decentralizing.
early 15c., decepcioun, "act of misleading, a lie, a falsehood," from Old French déception (13c., decepcion) or directly from Late Latin deceptionem (nominative deceptio) "a deceiving," noun of state or action from past-participle stem of Latin decipere "to ensnare, take in, beguile, cheat," from de "from" or pejorative (see de-) + capere "to take," from PIE root *kap- "to grasp."
From mid-15c. as "state of being deceived; error, mistake;" from 1794 as "artifice, cheat, that which deceives."
"tending to mislead or give false impression," 1610s, from French deceptif (late 14c.), from Medieval Latin deceptivus, from decept-, past participle stem of Latin decipere "to ensnare, take in, beguile, cheat," from de "from" or pejorative (see de-) + capere "to take," from PIE root *kap- "to grasp."
In this sense in English it superseded deceptious (c. 1600), from French deceptieux, from Medieval Latin deceptiosus, from deceptionem; also deceptory (mid-15c.), from Latin deceptorious. Related: Deceptively; deceptiveness.