gnarl (v.)

"contort, twist, make knotty," 1814, a back-formation from gnarled (q.v.). As a noun from 1824, "a knotty growth on wood." Earlier an identical verb was used imitatively in a sense of "to snarl" like a dog (1590s); Farmer and Henley ("Slang and Its Analogues") lists gnarler as thieves' slang for "a watch-dog."

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Definitions of gnarl from WordNet
gnarl (v.)
twist into a state of deformity;
The wind has gnarled this old tree
gnarl (v.)
make complaining remarks or noises under one's breath;
Synonyms: murmur / mutter / grumble / croak
gnarl (n.)
something twisted and tight and swollen;
the old man's fists were two great gnarls
Synonyms: knot