Green’s Dictionary of Slang

1. a yokel or simpleton.

1770		H. Clinker Hist. of the Haveral Wives (1799) 6: He has twa gilly gawkies o’ dochters.
1820		Comical Dialogue Between Maggy and Janet 10: If the gillie-gawkies shou’d come into the kirk wi’ their heels up an’ their heads down, our Mess John [,...] winna move his tongue.
1883		Nat. Police Gaz. (NY) 10 Nov. 6/2: ‘Are you such a gilly [...] that when you were dead on to him, you didn’t pull the rocks’.
1885		‘High School Sl.’ in N.Y. Dispatch 31 May 7: Do you know I think he’s a regular gillie?
1896		Ade Artie (1963) 55: Say, you must think I’m a prize gilly to set around here and give up my insides to you about her.
1898		Binstead & Wells Pink ’Un and Pelican 178: ’Is missis ’as ’ooked up with a gillie of an actor chap.
1904		C. Connors Bowery Life [ebook] Say, I thought dey’d need a rattler to move him. Rattler. You gilly, what do they cart a chaw off in when a collar gets tru beltin’ him, generally? A rattler is a patrol; dat’s what.
1910		‘O. Henry’ ‘The Poet and the Peasant’ in Strictly Business (1915) 79: The Central Office must be bughouse to send you out looking like such a gillie.
1920		Ade Hand-made Fables 307: Any small-sized Gillie can horn his way into a Chamber of Commerce or enlist as a Booster.
1939		in W.C. Fields By Himself (1974) 327: I’ll be the laughing stock of every gink in the town from now on – you have made me a gilly.

2. an outsider, an amateur, e.g. as regards confidence trickery, carnival work; also attrib.

1887		Ft Worth Dly Gaz. (TX) 29 Aug. 6/4: No gillie can do me, and that duck’s a macer sure’s you’re born.
1891		Omaha Dly Bee (NE) 5 Sept. 7/3: We told the gilly right on the spot he couldn’t play no second-hand newspaper stories.
1905		Little Falls Herald (MN) 31 Mar. 3/3: How to Operate the Shell Game with Profit [...] When the steerer gets the geezer in the push, let the boosters stall until the main plugger cops; then, if the gilly digs in his keyser [sic] or goes south for soft, give him a flash of the little dinkie doodle ball.
1909		W. Irwin Confessions of a Con Man 61: We lacked experienced men [...] it was all gilly help.
1943		J.A. Kirch ‘March of the Damned’ in Ten Detective Aces Mar. 🌐 But try to tell any gillie, much less a dumb sheriff, that. No outsider would get it.
2021		Breen & Conlon Hitmen 68: [of a drug courier] His method was to ring a gilly and direct him to a location.

3. (Polari) a woman, esp.as a member of an audience.

2019		P. Baker Fabulosa 293/1: gillies women (especially those in an audience).
2023		R. Milward Man-Eating Typewriter 121: [F]elching the trummuses of those destestable arroganki gillies and flatties.