Train bird to accept one sent back (7)
I believe the answer is:
retinue
'train' is the definition.
(people following someone in a procession)
'bird to accept one sent back' is the wordplay.
'bird' becomes 'ree' (term for a female ruff bird).
'to accept' indicates putting letters inside.
'one' becomes 'unit' (synonyms).
'sent back' is a reversal indicator.
'unit' written backwards gives 'tinu'.
'ree' placed around 'tinu' is 'RETINUE'.
(Other definitions for retinue that I've seen before include "Group of followers" , "Attendants, followers" , "Body of aides" , "Group of assistants" , "company" .)