Giant bird on a pole (5)
I believe the answer is:
titan
'giant' is the definition.
(I know that giant can be written as titan)
'bird on a pole' is the wordplay.
'bird' becomes 'tit' (tit is a kind of bird).
'on' means one lot of letters go next to another.
'pole' becomes 'n' (abbreviation for North, as in North Pole).
'tit'+'a'+'n'='TITAN'
(Other definitions for titan that I've seen before include "A giant; Saturn moon" , "very big" , "Saturn's largest satellite" , "One huge" , "Giant of Greek mythology" .)