The Collaborative International Dictionary of English v.0.48:
Knurly \Knurl"y\ (n[^u]rl"[y^]), [Compar. Knurlier
(n[^u]rl"[i^]*[~e]r); superl. Knurliest.] [See Knur, and
cf. Gnarly.]
Full of knots; hard; tough; hence, capable of enduring or
resisting much.
[1913 Webster]