Dog swallows minute creature (4)
I believe the answer is:
lamb
'creature' is the definition.
(lamb is a kind of creature)
'dog swallows minute' is the wordplay.
'dog' becomes 'lab' (short for labrador).
'swallows' is an insertion indicator.
'minute' becomes 'm' (abbreviation).
'lab' enclosing 'm' is 'LAMB'.
(Other definitions for lamb that I've seen before include "English essayist" , "author?" , "Tender sheep meat" , "Young ovine" , "Skipper" .)