gnarl

Short definition from Wiktionary

Noun

1. 1
   A knot in wood; a knurl or a protuberance with twisted grain, on a tree.
2. 2
   Something resembling a knot in wood, such as in stone or limbs.

Verb

1. 1
   To knot or twist something.
2. 2
   To snarl or growl; to gnar.

Adjective

1. 1
   Gnarled, knotty, twisted.