Nibblers taking bit from the front of clerical garment (4)
I believe the answer is:
mice
'nibblers' is the definition.
(animals which nibble)
'taking bit from the front of clerical garment' is the wordplay.
'taking bit from the front of' means to remove the first letter.
'clerical garment' becomes 'amice' (type of garment worn by a priest).
'amice' with its initial letter removed is 'MICE'.
(Other definitions for mice that I've seen before include "They'll play when the cat's away" , "Squeaking rodents" , "''Of ... and Men'' (John Steinbeck)" , "shy people" , "Blind group" .)