Giant bird with a pelican's tail (5)
I believe the answer is:
'giant' is the definition.
(titans are giant mythological creatures)
'bird with a pelican's tail' is the wordplay.
'bird' becomes 'tit' (tit is a kind of bird).
'with' is a charade indicator (letters next to each other).
'tail' suggests the final letters.
The final letter of 'pelican' is 'n'.
(Other definitions for titan that I've seen before include "Mythological giant" , "Moon of Saturn visited by the Huygens probe" , "Giant of Greek mythology" , "Giant -- rocket" , "Atlas, say" .)