Was sent back by William Bird (7)
I believe the answer is:
sawbill
'bird' is the definition.
(sawbill is a kind of bird)
'was sent back by william' is the wordplay.
'sent back' shows that the letters should be reversed in order.
'by' means one lot of letters go next to another.
'william' becomes 'bill'.
'was' back-to-front is 'saw'.
'saw'+'bill'='SAWBILL'
(Other definitions for sawbill that I've seen before include "diver" , "Flyer" .)