The Collaborative International Dictionary of English v.0.48:

Grub \Grub\ (gr[u^]b), v. i. [imp. & p. p. Grubbed (gr[u^]bd),
   p. pr. & vb. n. Grubbing.] [OE. grubbin., cf. E. grab,
   grope.]
   1. To dig in or under the ground, generally for an object
      that is difficult to reach or extricate; to be occupied in
      digging.
      [1913 Webster]

   2. To drudge; to do menial work. --Richardson.
      [1913 Webster]