The Collaborative International Dictionary of English v.0.48:

Nibble \Nib"ble\, v. t. [imp. & p. p. Nibbled; p. pr. & vb. n.
   Nibbling.] [Cf. Nip.]
   To bite by little at a time; to seize gently with the mouth;
   to eat slowly or in small bits.
   [1913 Webster]

         Thy turfy mountains, where live nibbling sheep. --Shak.
   [1913 Webster]