Green’s Dictionary of Slang

a horse.

1886		M.E. Kennard Girl in the Brown Habit I 15: I suppose our ‘gees’ will jump all right.
1889		Dead Bird (Sydney) 2 Nov. 7/4: A two-year-old’s running may sometimes be bad, / And you vow for that ‘gee’ you will never more vote.
1894		A. Hope Dolly Dialogues 20: You can’t go ridin’ without gees can you?
1897		Truth (Sydney) 10 Jan. 5/3: I’m but the worried owner of just half-a-dozen gees.
1900		Sporting Times 17 Feb. 1/2: What the deuce do we care, boy, what jacket you wear / When your gee is the first past the post.
1908		Sun. Times (Perth) 21 June 4/8: Goes the gun [i.e. swindler] where goes the gee, / Goes the thimble, goes the pea.
1910		‘Doss Chiderdoss’ ‘Wait and See!’ Sporting Times 9 Apr. 1/3: I can turn a smilin’ face / On the bloke who likes a flutter on a gee.
1914		C. Holme Lonely Plough (1931) 169: He preferred the old gee to all the petrol-puffers in creation.
1936		W. Holtby South Riding (1988) 278: When you want a little spot cash, all you’ve got to do is to sell a gee or something.
1953		A.J. Liebling Honest Rainmaker (1991) 17: Mr. ‘Kid’ Bloggs [...] a smart Handicapper of the Gees.