Source : Webster's Revised Unabridged Dictionary (1913)

Gnarl \Gnarl\, n. [See {Gnar}, n.]
   a knot in wood; a large or hard knot, or a protuberance with
   twisted grain, on a tree.

Gnarl \Gnarl\, v. i. [imp. & p. p. {Gnarled}; p. pr. & vb. n.
   {Gnarling}.] [From older gnar, prob. of imitative origin; cf.
   G. knarren, knurren. D. knorren, Sw. knorra, Dan. knurre.]
   To growl; to snarl.

         And wolves are gnarling who shall gnaw thee first.
                                                  --Shak.

Source : WordNet®

gnarl
     n : something twisted and tight and swollen; "their muscles
         stood out in knots"; "the old man's fists were two great
         gnarls"; "his stomach was in knots" [syn: {knot}]
     v 1: twist into a state of deformity; "The wind has gnarled this
          old tree"
     2: make complaining remarks or noises under one's breath; "she
        grumbles when she feels overworked" [syn: {murmur}, {mutter},
         {grumble}, {croak}]