decadence n.

active word-forming element in English and in many verbs inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin, usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words.

As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative — "not, do the opposite of, undo" — which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), de-escalate (1964), etc. In some cases, a reduced form of dis-.

Proto-Indo-European root meaning "to fall."

It forms all or part of: accident; cadaver; cadence; caducous; cascade; case (n.1); casual; casualty; casuist; casus belli; chance; cheat; chute (n.1); coincide; decadence; decay; deciduous; escheat; incident; occasion; occident; recidivist.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit sad- "to fall down;" Latin casus "a chance, occasion, opportunity; accident, mishap," literally "a falling," cadere "to fall, sink, settle down, decline, perish;" Armenian chacnum "to fall, become low;" perhaps also Middle Irish casar "hail, lightning."

"in a state of decline or decay (from a former condition of excellence)," 1837 (Carlyle), 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:

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.

As a noun, "one whose artistic or literary work is supposed to show marks of decadence," 1889 (from 1887 as a French word in English), originally in a French context.

On the subject of poetry I am bound to signalize one of those grotesque, unexpected apparitions which would appear to be constitutional to our country [i.e. France] .... I refer to the recent appearance of a literary clique of madmen or idlers, the self-named décadents. I own I am almost ashamed to occupy your time with this unworthy subject, which I should not have thought fit to introduce had not our newspapers and even our reviews taken the décadents to task, and were it not that they have furnished chroniqueurs short of copy with matter for articles, and that the serious Temps itself has taken up their trashy nonsense. [The Athenaeum, Jan. 1, 1887]