Green’s Dictionary of Slang

1. a drunk, who sits around in a bar sleeping off the drink or generally wasting time.

1868		Oregon State Journal 19 Dec. 2/5: ‘Sitters,’ as they are called, [...] sit about on chairs [in saloons] to sleep off the effects of drink [DA].
1905		J.M. Richards With John Bull and Jonathan 139: The greater privacy of the hotels in England greatly impressed me, as no ‘loungers,’ or ‘sitters’ as they are called in America, are allowed to frequent them [DA].
1949		Eve. News (Sydney) 16 Feb. cited in Partridge DSUE (1984).

2. (US) a tramp who, lacking any alternative accommodation, sits in a tenement hallway.

1890

J.A. Riis How the Other Half Lives (1971) 64: On hot summer nights it is no rare experience [...] to find the hallways [of tenements] occupied by rows of ‘sitters,’ tramps whom laziness or hard luck has prevented from earning enough by their day’s ‘labor’ to pay the admission fee to a stale-beer dive, and who have their reasons for declining the hospitality of the police station lodging-room.

3. (US) a part-time prostitute.

1887		Lantern (N.O.) 9 Apr. 3: A certain class of young women go there as sitters, some even work out during the day and come here at night.
1971		Winick & Kinsie Lively Commerce 182: During the depression of the 1930’s [...] a number of houses featured ‘sitters,’ married women who worked from 1 to 4 p.m.
1989		J. Morton Lowspeak.

4. (US) a homeless person, employed by a tavern to sit near the fire and shiver in an obvious way so that kind-hearted patrons would buy them drinks (thus profiting the tavern).

1891		J.A. Riis How the Other Half Lives 77: As ‘sitters’ they occasionally find a job in the saloons about Chatham and Pearl Streets on cold winter nights, when the hallway is not practicable, that enables them to pick up a charity drink now and then and a bite of an infrequent sandwich. The barkeeper permits them to sit about the stove and by shivering invite the sympathy of transient customers.
1938		S. Hart New Yorkers 183: Bowery barkeeps employed homeless men and women as ‘sitters’ to shiver near the fire on wintry nights and thus evoke the sympathy of cash customers who would treat them to drinks to the great profit of the house [DA].

5. (US) the buttocks, the posterior.

1944

E. Wilson 11 Dec. [synd. col.] Joan Fontaine kicked on her sitter! ‘I kciked her square in the derreiere,’ confided Producer David P. Lewis.

6. a woman who frequents a tavern or nightclub and who receives a percentage on the drinks she gets male patrons to buy.

1948		Mencken Amer. Lang. Supplement II 682: Women who frequent taverns or night-clubs, getting a percentage on the drinks they induce male patrons to buy, are...sitters.
1959		‘Monroe Fry’ Sex, Vice & Business 24: Baltimore has an ordinance against B-girls, who are legally termed ‘sitters.’ To circumvent this ordinance, many proprietors put the ladies on the payroll [. . .] which magically changes them from ‘sitters’ into ‘hostesses’.
1972		B. Rodgers Queens’ Vernacular 159: sitter a whore who cadges drinks in a bar. Syn: B-girl.
1986–7		Maledicta IX 150: The original argot of prostitution includes some words and phrases which have gained wider currency and some which have not […] sitters (B[ar]-girls).