Male swan (3)
I believe the answer is:
cob
'male swan' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for cob that I've seen before include "Horse, male swan and loaf of bread" , "Hazelnut" , "Round loaf of bread" , "Source of bread" , "A loaf; a nut; a horse" .)