The Collaborative International Dictionary of English v.0.48:

Knab \Knab\ (n[a^]b), v. t. [imp. & p. p. Knabbed (n[a^]bd);
   p. pr. & vb. n. Knabbing.] [See Nab, v. t., and cf.
   Knap, v. t.]
   1. To seize with the teeth; to gnaw. "Knabbing crusts."
      [Obs.] --L'Estrange.
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   2. To nab. See Nab, v. t. [Colloq.]
      [1913 Webster]