Green’s Dictionary of Slang

1. a petty thief.

1812		Vaux Vocab. of the Flash Lang.
1855		Commercial Jrnl (Dublin) 15 Dec. 2/3: Then woe to the tribe of pickers and stealers, / Nibblers ands gnawers and evil dealers!
1859, 1860		Hotten Dict. of Modern Sl. etc.
1873		Sl. Dict.
1889–90		Barrère & Leland Dict. of Sl., Jargon and Cant.

2. (US Und.) a fellator.

1950		Goldin et al. DAUL 145/1: Nibbler. A male oral sodomist.
1972		B. Rodgers Queens’ Vernacular 52: fellator [...] nibbler (’40s–’50s).