英语词源字典 - 在线词源网站

babysit (v.)[babysit 词源字典]: also baby-sit, 1947, from baby (n.) + sit (v.); figurative use (often contemptuous) by 1968. Babysitting is from 1946.[babysit etymology, babysit origin, 英语词源]
babysitter (n.): also baby-sitter, 1914, from baby (n.) + agent noun from sit (v.). Short form sitter is attested from 1937.
sit (v.): Old English sittan "to occupy a seat, be seated, sit down, seat oneself; remain, continue; settle, encamp, occupy; lie in wait; besiege" (class V strong verb; past tense sæt, past participle seten), from Proto-Germanic *setjan (cognates: Old Saxon sittian, Old Norse sitja, Danish sidde, Old Frisian sitta, Middle Dutch sitten, Dutch zitten, Old High German sizzan, German sitzen, Gothic sitan), from PIE root *sed- (1) "to sit" (see sedentary).

With past tense sat, formerly also set, now restricted to dialect, and sate, now archaic; and past participle sat, formerly sitten. In reference to a legislative assembly, from 1510s. Meaning "to baby-sit" is recorded from 1966.

To sit back "be inactive" is from 1943. 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 1650s. Sitting pretty is from 1916.
sitter (n.): c. 1300, "one that sits," agent noun from sit (v.). As short for baby-sitter from 1937.