sit (v.) Look up sit at Dictionary.com
Old English sittan "to be seated, to seat oneself" (class V strong verb; past tense sæt, past participle seten), from Proto-Germanic *setjanan (cf. Old Saxon sittian, Old Norse sitja, Old Frisian sitta, Middle Dutch sitten, Dutch zitten, Old High German sizzan, German sitzen, Gothic sitan), from PIE root *sed- "to sit" (see sedentary).

In reference to a legislative assembly, from 1510s. Meaning "to baby-sit" is recorded from 1966. Sitting room first recorded 1771. Slang sitting duck "easy target" first recorded 1944; literal sense is from 1867 (it is considered not sporting to shoot at one). Sitting pretty is from 1916. To sit on one's hands was originally "to withhold applause" (1926); later, "to do nothing" (1959). To sit around "be idle, do nothing" is 1915, American English. To sit out "not take part" is from 1620s.