Green’s Dictionary of Slang

1. lit. or fig. hunger, appetite.

1832

Satirist (London) 22 Jan. 29/3: Walk here, walk here, and larn the terms, / And let us of your ‘nibble’ ease you; / For, out of all the butcher firms, Mellish and Co. are sure to please you!

2. an opportunity for gain or theft.

1852		‘Epistle from Joe Muggins’s Dog’ in Era (London) 1 Feb. 4/1: We gets the hods afore the day iz hout at tens to sunmet like a kipple ov poneys, and that’l be no nasty nibble, if we mix it,.
1865		Leaves from Diary of Celebrated Burglar 44/1: Charley the Flat (!) saw a rare nibble in this case, and forthwith ‘slung his bait’.

3. (US) a sip, a mouthful.

1950

R. Starnes Another Mug for the Bier 89: He took a generous nibble at his drink and continued.

4. a non-committal enquiry, casual conversation.

1980

(con. 1974) W. Sherman Times Square 253: Joe was tiring of the ‘nibble.’ He told Mack that it was time to get down to business.