Giant bird article (5)
I believe the answer is:
titan
'giant' is the definition.
(titans are giant mythological creatures)
'bird article' is the wordplay.
'bird' becomes 'tit' (tit is a kind of bird).
'article' becomes 'an' (indefinite article).
'tit'+'an'='TITAN'
(Other definitions for titan that I've seen before include "enormous thing" , "Largest satellite of Saturn" , "An old Greek god - Atlas was one" , "Colossus" , "One of the first pantheon of Greek deities" .)