Green’s Dictionary of Slang

1. a fool, an unsophisticated person, a peasant.

1899		Ade Fables in Sl. (1902) 75: An Illinois Squab came home from Business College with a Zebra Collar and a pair of Tan Shoes big enough for a Coal Miner.
1904		A. Lang in L.A. Times 29 Mar. 7: Of course, there is no reason why I should know what [...] a ‘squab,’ a ‘yap,’ a ‘spaghetti joint,’ a ‘graft,’ and so forth, mean.
1910		Wodehouse Psmith in the City (1993) 50: I also am a worker. A toiler, not a flatfish. A sizzler, not a squab.

2. a young woman.

1909		Goodwin’s Wkly (Salt Lake City, UT) 25 Dec. 5/2: Jim got to handing out tiaras to every squab and broiler on Broadway.
1911		Indianapolis Star 2 Aug. 5: Stage hands, who were anxious to learn the prevailing words of slang of the season, stood with their jaws agape during the afternoon when the chorus girls twisted the English language into hard knots for their benefit. [...] ‘We are not going to be chorus girls, dears, warblers, chickens, quails or squabs any longer. The correct dope this year is [...] quims.’.
1917		O.O. McIntyre New York Day by Day 17 Sept. [synd. col.] As she passed [...] someone called out: ‘Some squab’ which being interpreted into Manhattanese means ‘Easy to look at’.
1927		W.R. Morse ‘Stanford Expressions’ in AS II:6 278: squab—a young girl.
1938		D. Runyon ‘All Horse Players Die Broke’ in Runyon on Broadway (1954) 707: I suppose I am dull company for a squab.
1943		Chicago Trib. Graphic Section 26 Dec. 7/1: Jive Talk [...] Smooth Girl Slick chick. Sweet stuff. Wolf bait. Queen of hearts. P-38. Able Grable. A good deal. A doll. Smooth potato. Hot gingerbread. Pretty pigeon. 20-20 little squab.
1951		(con. 1913) Green & Laurie Show Biz from Vaude to Video 34: When Gertrude Hoffman’s new shop opened [...] her ad was replete with the new slang of the day, referring to the girls in the show as ‘chickens,’ ‘squabs’ and ‘broilers’.
1966		Trimble 5000 Adult Sex Words and Phrases.