Etymology
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sound (v.1)

early 13c., sounen "to be audible, produce vibrations affecting the ear," from Old French soner (Modern French sonner) and directly from Latin sonare "to sound, make a noise" (from PIE root *swen- "to sound"). From late 14c. as "cause something (an instrument, etc.) to produce sound." Related: Sounded; sounding.

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sound (n.2)
"narrow channel of water," c. 1300, from Old Norse sund "a strait, swimming," or from cognate Old English sund "act of swimming, stretch of water one can swim across, a strait of the sea," both from Proto-Germanic *sundam-, from *swum-to-, suffixed form of Germanic root *swem- "to move, stir, swim" (see swim (v.)).
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sound (adj.)
"free from special defect or injury," c. 1200, from Old English gesund "sound, safe, having the organs and faculties complete and in perfect action," from Proto-Germanic *sunda-, from Germanic root *swen-to- "healthy, strong" (source also of Old Saxon gisund, Old Frisian sund, Dutch gezond, Old High German gisunt, German gesund "healthy," as in the post-sneezing interjection gesundheit; also Old English swið "strong," Gothic swinþs "strong," German geschwind "fast, quick"), with connections in Indo-Iranian and Balto-Slavic. Meaning "right, correct, free from error" is from mid-15c. Meaning "financially solid or safe" is attested from c. 1600; of sleep, "undisturbed," from 1540s. Sense of "holding accepted opinions" is from 1520s.
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sound (v.2)
"fathom, probe, measure the depth of," mid-14c. (implied in sounding), from Old French sonder, from sonde "sounding line," perhaps from the same Germanic source that yielded Old English sund "water, sea" (see sound (n.2)). Barnhart dismisses the old theory that it is from Latin subundare. Figurative use from 1570s.
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sound (n.1)

"noise, what is heard, sensation produced through the ear," late 13c., soun, from Old French son "sound, musical note, voice," from Latin sonus "sound, a noise," from PIE *swon-o-, from root *swen- "to sound."

The unetymological -d was established c. 1350-1550 as part of a tendency to add -d- after -n-. Compare gender (n.), thunder (n.), jaundice (n.), spindle, kindred, riband, and, from French powder (n.), meddle, tender (adj.), remainder, dialectal rundel, rundle for runnel, etc. First record of sound barrier is from 1939. Sound check is from 1977; sound effect is 1909, originally live accompaniment to silent films.

The experts of Victor ... will ... arrange for the synchronized orchestration and sound effects for this picture, in which airplane battles will have an important part. [Exhibitor's Herald & Moving Picture World, April 28, 1928]
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off (prep., adv.)

by c. 1200 as an emphatic form of Old English of (see of), employed in the adverbial use of that word. The prepositional meaning "away from" and the adjectival sense of "farther" were not firmly fixed in this variant until 17c., but once they were they left the original of with the transferred and weakened senses of the word. Meaning "not working" is from 1861.

Off the cuff "extemporaneously, without preparation" (1938) is from the notion of speaking from notes written in haste on one's shirt cuffs. In reference to clothing, off the rack (adj.) "not tailored, not made to individual requirements, ready-made" is by 1963, on the notion of buying it from the rack of a clothing store; off the record "not to be publicly disclosed" is from 1933; off the wall "crazy" is 1968, probably from the notion of a lunatic "bouncing off the walls" or else in reference to carom shots in squash, handball, etc.

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off (v.)
"to kill," 1930, from off (adv.). Earlier verbal senses were "to defer" (1640s), "to move off" (1882). Related: Offed.
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re-sound (v.)

"sound anew, sound (a letter, music note) again," 1897, from re- "again" + sound (v.1). Spelled with a hyphen to distinguish it from resound (v.). Related: Re-sounded; re-sounding.

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far-off (adj.)
also faroff, "distant, remote," 1590s, from adverbial phrase, from far (adv.) + off (adv.).
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