c. 1600, "action of adapting (something to something else)," from French adaptation, from Late Latin adaptationem (nominative adaptatio), noun of action from past-participle stem of adaptare "to adjust," from ad "to" (see ad-) + aptare "to join," from aptus "fitted" (see apt).
The meaning "condition of being adapted, state of being fitted to circumstances or relations" is from 1670s. The sense of "modification of a thing to suit new conditions" is from 1790. The biological sense of "variations in a living thing to suit changed conditions" is by 1859, in Darwin's writings.
1801, "one who adapts (something to something else)," agent noun from adapt. From 1808 as "mechanical means of adapting objects so they fit or work together" (originally of chemistry apparatus); electrical engineering sense is by 1907.
late 14c., "to join or unite (something to something else)," from Latin addere "add to, join, attach, place upon," literal and figurative, from ad "to" (see ad-) + -dere, combining form meaning "to put, place," from dare "to give" (from PIE root *do- "to give").
The intransitive meaning "to do sums, do addition" also is from late 14c. Related: Added; adding. To add up is from 1754; in the figurative meaning "make sense," by 1942. Adding machine "machine to cast up large sums" is from 1822.
1794, "an appendix to a work; a thing to be added," from Latin addendum, neuter of addendus "that which is to be added," gerundive of addere "add to, join, attach" (see add (v.)). The classical plural form is addenda.
Middle English naddre, from Old English (West Saxon) næddre (Mercian nedre, Northumbrian nedra), "a snake; the Serpent in the Garden of Eden," from Proto-Germanic *naethro "a snake" (source also of Old Norse naðra, Middle Dutch nadre, Old High German natra, German Natter, Gothic nadrs), from PIE root *nētr- "snake" (source also of Latin natrix "water snake" (the sense is probably by folk-association with nare "to swim"); Old Irish nathir, Welsh neidr "snake, serpent").
The modern form represents a faulty separation 14c.-16c. of a nadder into an adder, for which see also apron, auger, nickname, orange, humble pie, aitchbone, umpire. Nedder is still a northern English dialect form.
Since Middle English the word has been restricted to use as the common name of the viper, the only poisonous British reptile (though not generally fatal to humans), then by extension it was applied to venomous or similar snakes elsewhere (puff-adder, etc.). Folklore connection with deafness is via Psalms lviii.1-5. The adder is said to stop up its ears to avoid hearing the snake charmer called in to drive it away.
1530s (implied in addicted) "to devote or give up (oneself) to a habit or occupation," from Latin addictus, past participle of addicere "to deliver, award, yield; make over, sell," properly "give one's assent to," but figuratively "to devote, consecrate; sacrifice, sell out, betray, abandon." This is from ad "to" (see ad-) + dicere, which was usually "to say, declare" (from PIE root *deik- "to show," also "pronounce solemnly"), but also could be "adjudge, allot."
"It is a yielding to impulse, and generally a bad one" [Century Dictionary]. Old English glossed Latin addictus literally with forscrifen. Related: Addicted; addicting.