soundtrack n.

"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.

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]

late 15c., "footprint, mark left by anything," from Old French trac "track of horses, trace" (mid-15c.), possibly from a Germanic source (compare Middle Low German treck, Dutch trek "drawing, pulling;" see trek). Meaning "lines of rails for drawing trains" is from 1805. Meaning "branch of athletics involving a running track" is recorded from 1905. Meaning "single recorded item" is from 1904, originally in reference to phonograph records. Meaning "mark on skin from repeated drug injection" is first attested 1964.

Track record (1955) is a figurative use from racing, "performance history" of an individual car, runner, horse, etc. (1907, but the phrase was more common in sense "fastest speed recorded at a particular track"). To make tracks "move quickly" is American English colloquial first recorded 1835; to cover (one's) tracks in the figurative sense first attested 1898; to keep track of something is attested from 1883. American English wrong side of the tracks "bad part of town" is by 1901. Track lighting attested from 1970.