Bird with some backward possibilities (4)
I believe the answer is:
ibis
'bird' is the definition.
(ibis is a kind of bird)
'some backward possibilities' is the wordplay.
'backward' says the letters should be written in reverse.
'some' indicates a hidden word (some parts of the word are used).
'sibi' is hidden within 'possibilities'.
'sibi' written backwards gives 'IBIS'.
'with' acts as a link.
(Other definitions for ibis that I've seen before include "may be sacred?" , "Wader once sacred in Egypt" , "Wading bird with a down-curved bill" , "Storklike bird" , "Long-legged wading bird" .)