A sheep you heard (3)
I believe the answer is:
ewe
'a sheep' is the definition.
(a ewe is a female sheep)
'you heard' is the wordplay.
'heard' shows a homophone (sound like).
'you' is a homophone of 'EWE'.
(Other definitions for ewe that I've seen before include "Lamb supplier" , "Female ovine" , "Female on farm" , "Palindrome for a female sheep" , "Farm animal" .)