set (v.) Look up set at Dictionary.com
Old English settan "cause to sit, put in some place, fix firmly," from Proto-Germanic *satjanan (cf. Old Norse setja, Old Frisian setta, Dutch zetten, German setzen), causative form of Proto-Germanic root *set- (cf. Old English sittan "to sit," see sit (v.)).

Confused with sit since early 14c. Of the sun, moon, etc., "to go down," recorded from c.1300. Set-to "bout, fight" is 1743, originally pugilistic slang. Setup "arrangement" is from 1890.
set (adj.) Look up set at Dictionary.com
"fixed," from Middle English sett, properly past participle of setten "to set" (see set (v.)). Meaning "ready, prepared" first recorded 1844.
set (n.) Look up set at Dictionary.com
"collection of things," mid-15c., from Old French sette "sequence," variant of secte, from Medieval Latin secta "retinue," from Latin secta "a following" (see sect). The word had been earlier used in English in the sense of "religious sect" (late 14c.), which likely is the direct source of some meanings, e.g. "group of persons with shared status, habits, etc." (1680s). Sense of "burrow of a badger" is attested from 1898. That of "scenery for an individual scene in a play, etc." is recorded from 1859. Meaning "group of pieces musicians perform at a club during 45 minutes (more or less) is from c.1925, though it is found in a similar sense in 1580s.