Sinbad's bird (3)
I believe the answer is:
roc
'sinbad's bird' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for roc that I've seen before include "Mythical creature from Arabia" , "Gigantic bird of eastern legend - cor!" , "Vast legendary bird" , "Big bird" , "Bird imagined" .)