Sound heard by a shepherd (3)
I believe the answer is:
baa
'sound heard by a shepherd' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for baa that I've seen before include "to Heathrow, the operators" , "Lamb's cry" , "Beastly sound f" , "Sound from a ewe" , "Sheep's bleat" .)