Old English deaf "lacking the sense of hearing," also "empty, barren," from Proto-Germanic *daubaz (source also of Old Saxon dof, Old Norse daufr, Old Frisian daf, Dutch doof "deaf," German taub, Gothic daufs "deaf, insensate"), from PIE dheubh-, which was used to form words meaning "confusion, stupefaction, dizziness" (source also of Greek typhlos "blind," typhein "to make smoke;" Old English dumb "unable to speak;" Old High German tumb).
The word was pronounced to rhyme with reef until 18c. Meaning "refusing to listen or hear" is from c. 1200. As a noun, "deaf persons," from c. 1200. Deaf-mute is from 1837, after French sourd-muet. Deaf-mutes were sought after in 18c.-19c. Britain as fortune-tellers. Deaf as an adder (Old English) is from Psalms lviii.5.
1590s, "to make deaf," from deaf + -en (1). The earlier verb was simply deaf (mid-15c.). For "to become deaf, to grow deaf," Old English had adeafian (intransitive), which survived into Middle English as deave but then took on a transitive sense from mid-14c. and sank from use except in dialects (where it mostly has transitive and figurative senses), leaving English without an intransitive verb here. Related: Deafened.
"plainly illogical," 1550s, from French absurde (16c.), from Latin absurdus "out of tune, discordant;" figuratively "incongruous, foolish, silly, senseless," from ab- "off, away from," here perhaps an intensive prefix, + surdus "dull, deaf, mute," which is possibly from an imitative PIE root meaning "to buzz, whisper" (see susurration). Thus the basic sense is perhaps "out of tune," but de Vaan writes, "Since 'deaf' often has two semantic sides, viz. 'who cannot hear' and 'who is not heard,' ab-surdus can be explained as 'which is unheard of' ..." The modern English sense is the Latin figurative one, perhaps "out of harmony with reason or propriety." Related: Absurdly; absurdness.
"inept person; stupid, dull old man," 1842, especially "bad golfer" (by 1875), perhaps from Scottish duffar "dull or stupid person," from dowf "stupid," literally "deaf," from Old Norse daufr, with pejorative suffix -art. Or perhaps from 18c. thieves' slang duff (v.) "to dress or manipulate an old thing and make it look new," hence duffer "one who sells spurious goods at high prices" (1766).
"simple, wanting in intelligence," also "crazy, mad," 1884, perhaps from daft (adj.), or from obsolete daffe "a halfwit" (early 14c.; mid-13c. as a surname), which survived in 19c. in dialects, itself of uncertain origin (OED finds a proposed origin in Scandinavian words for "deaf, stupid," such as Old Norse daufr, "phonetically inadmissible"). Compare late 15c. daffish "dull-witted, spiritless." With -y (2). Related: Daffily; daffiness. The Warner Bros. cartoon character Daffy Duck debuted in 1937.