Green’s Dictionary of Slang

gill n.1

also gil
[ety. unknown]

1. (also gills) a gullible person.

[UK]W. Warner Albion’s England Bk 7 xxxvii n.p.: The simplest Gill or Knave [F&H].
[UK]J. Day Blind Beggar of Bednall-Green Act I: Ha, ha, ha, gill, gill, gill, I have been ready to burst. Son pray thee tell me how thou laid’st this plot?
implied in rum gill under rum adj.
[UK]Vaux Vocab. of the Flash Lang. in McLachlan (1964) 243: gill a word used by way of variation, similar to cove, gloak or gory; but generally coupled to some other descriptive term as a flash-gill, a toby-gill.
[US]Cincinnati Enquirer 7 Sept. 10/7: Gill – The man who backs the ‘snaps’ – a party with a few dollars, no brains and less experience in the show business. He always returns a sadder, wiser, broke-up man, his shekels gone, and the only satisfaction left of being added as one to the number of gills.
[US]Daily Trib. (Bismarck, ND) 23 Oct. 4/1: Those people who [...] haunt stage doors [...] are ‘gillies,’ ‘gills,’ ‘guys,’ ‘chappies,’ ‘mashers,’ ‘chumps,’ ‘lunkheads’ and ‘lugs.’.
[US] ‘Jargon of the Und.’ in DN V 447: Gill, A credulous person.
[US]H.C. Witwer Yes Man’s Land 307: Jack and Maxim had put the fear of the Lord into this double-crossing gil and he was now house broke.
[US]G. & S. Lorimer Stag Line 161: I hadda loan Mosey my roll to flash on the gills at the Carny.
[Ire]B. Behan Scarperer (1966) 106: Your gills here, he says he doesn’t understand English.

2. (also gillie) a general term for a man.

[UK] ‘A Leary Mot’ in Farmer Musa Pedestris (1896) 77: Now Moll’s flash com-pan-ion was a Chick-lane gill, and he garter’d below his knee.
[UK]‘An Amateur’ Real Life in London I 596: You will here have to mingle with some of the queer Gills and rum Covies of all ranks.
[UK]W.T. Moncrieff Heart of London II i: I haven’t a downier gill in the whole college than you are.
[UK]Flash Dict. in Sinks of London Laid Open.
[US]Cairo Bull. (Cairo, IL) 5 Nov. 2/3: [from The Graphic, London] Farewell, gonnoffs and gnostics all, / And gillies sweet and free.
[US]H.C. Witwer Fighting Blood 141: I’ve tried everything I know to get this gil to fight us and no can do!
[US]T. Thursday ‘And Howe’ in Everybody’s Feb. [Internet] That gil you wished on me would of been okay lecturing at Yale and Harvard.
[US]Roosevelt Sykes ‘Papa Sweetback Blues’ [lyrics] He don’t work, he call himself a smart gill, / He don’t care about nobody.

3. an interfering person.

[UK]‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc. 87: A Gil is he who pokes in his nose unasked, as if authoritatively. Gil Gill, was a beadle of Farringdon-within.

4. (UK Und.) oneself.

[UK]P.H. Emerson Signor Lippo 47: We could have the small room with two letties to our own gills.

In phrases

his gills (n.) (also her gills, his jills)

(usu. Aus.) a self-important person, an authority, ‘his nibs’.

[Aus]Dead Bird (Sydney) 21 Dec. 8/4: And now to look just like his gills, / The clerks, and dudes, and mashers, / Are shaving of their side levers.
[Aus]Melbourne Punch 25 Feb. 4/4: I think she’ll be too many for his gills.
[UK]Illus. Police News 12 Apr. 4/4: But she cares for his gills not a rap!
[Aus]Sun. Times (Perth) 28 Aug. 4/7: ‘Well, look here,’ proceeded the she-peb, ‘when this ’ere rot’s over arst ’ees gills to play a cake walk’.
[Aus]E. Dyson Fact’ry ’Ands 242: Et this point up comes his gills, the junior partner, Duff.
[Aus]E. Dyson ‘Dukie M’Kenzie’s Dawnce’ Benno and Some of the Push 36: She ups with ’er trunk, sniffs at me, ’n’ sez her gills ’No conversation, if yeh please!’ she sez. [...] ‘Have a look et his gills,’ the packer continued.
[Aus]E. Dyson ‘Weepin’ Willie’ ‘Hello, Soldier!’ 49: But his jills would sniff ’n’ shiver in the mother of a fright.