Little critter (4)
I believe the answer is:
mite
'little critter' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for mite that I've seen before include "The widow's small donation" , "The widow's contribution, just in time" , "The widow's small offering" , "The Biblical widow's offering" , "Tiny creature found in food" .)