Giant bird, and tailless (5)
I believe the answer is:
titan
'giant' is the definition.
(synonyms)
'bird and tailless' is the wordplay.
'bird' becomes 'tit' (tit is a kind of bird).
'tailless' means to remove the last letter (the tail of the word is removed).
'and' with its final letter taken off is 'an'.
'tit'+'an'='TITAN'
(Other definitions for titan that I've seen before include "immense figure" , "Taint (anag.)" , "Atlas, say" , "Prometheus, for instance" , "Hyperion, for example" .)