Real Dictionary

grub
countable noun: A grub is a young insect which has just come out of an egg and looks like a short fat worm.
uncountable noun: Grub is food.
verb: If you grub around, you search for something.

grub in American English
the short, fat, wormlike larva of certain insects, esp. of a beetle
to clear (ground) of roots and stumps by digging them up
to dig in the ground
intransitive verb: to dig; search by or as if by digging
noun: the thick-bodied, sluggish larva of several insects, as of a scarab beetle
transitive verb: to dig; clear of roots, stumps, etc

grub in British English
noun: the short legless larva of certain insects, esp beetles
verb: to search for and pull up (roots, stumps, etc) by digging in the ground