Green’s Dictionary of Slang

1. ‘a hard-hearted or savage person’ (Hotten 1859).

1859, 1860		Hotten Dict. of Modern Sl. etc.
1861		(con. 1840s–50s) H. Mayhew London Labour and London Poor I 315/1: He had a butler, a regular ‘knark,’ who was a b— and a half.
1864, 1867, 1870		Hotten Sl. Dict.

2. see nark n.¹