waiter, n. — Green’s Dictionary of Slang

waiter n.

[it ‘waits’ for the rest of the field to finish; Stephens & O’Brien, Materials for a Dict. of Aus. Slang (ms.; 1900–10), suggest that the owner is waiting for a more profitable race or deliberately running the horse badly so as to improve its handicapping in another race]

(Aus.) a losing horse.

1885		Bulletin (Sydney) 31 Jan. 14/3: Good authorities declare that the proper place to spot a winner of a coming handicap, is to plant oneself down in the home turn at a previous meet, and then note the gallant army of ‘waiters,’ or stiff ’uns just sent out for a flutter to fool all future handicappers.
1900–10		Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 165: WAITER sporting slang a horse started in a race without any intention of winning.