The Collaborative International Dictionary of English v.0.48:

Gnar \Gnar\, n. [OE. knarre, gnarre, akin to OD. knor, G.
   knorren. Cf. Knar, Knur, Gnarl.]
   A knot or gnarl in wood; hence, a tough, thickset man; --
   written also gnarr. [Archaic]
   [1913 Webster]

         He was . . . a thick gnarre.             --Chaucer.
   [1913 Webster]