Old poet's pigeon (5)
I believe the answer is:
homer
This clue is a double definition.
'old poet's' is the first definition.
(ancient poet)
'pigeon' is the second definition.
(homer is a kind of pigeon)
(Other definitions for homer that I've seen before include "linesman" , "Great Greek who wrote The Iliad" , "Bart Simpson's father" , "Great Greek who was known to nod" , "messenger of war?" .)