"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 (see D).

Sound-board, "thin, resonant plate of wood in a musical instrument," is from 15c. Sound-wave "wave in an elastic medium by which sound spreads" is by 1848. Sound barrier, in reference to supersonic flights, is from 1939. Sound check is by 1977; sound effect is by 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]

"healthy, not diseased, free from special defect or injury," c. 1200, sounde, 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"). The German words have connections in Indo-Iranian and Balto-Slavic.

Paired alliteratively with safe (adj.) at least from c. 1300. The meaning "right, correct, free from error, in accord with facts" is from mid-15c. The sense of "holding accepted opinions" is from 1520s. Of arguments, etc., "without logical flaw," 1570s. The meaning "financially solid or safe" is attested from c. 1600; of sleep, "undisturbed, unbroken," from 1540s.

"fathom, probe, measure the depth of water" with or as if with a sounding line and lead, 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, "examine, discover or attempt to discover that which is concealed."

"narrow channel of water," c. 1300, sounde, 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 a suffixed form of Germanic *swem- "to move, stir, swim" (see swim (v.)). In Middle English it still could mean "swimming, the ability to swim."

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"). It is attested from late 14c. as "cause something (an instrument, etc.) to produce sound." Related: Sounded; sounding. A sounding-board originally was "canopy over a pulpit to direct the voice toward the audience" (1766). It also has been used in the "musical instrument sound-board" sense.