Huge bird I can train (7)
I believe the answer is:
titanic
'huge' is the definition.
(I've seen this before)
'bird i can train' is the wordplay.
'bird' becomes 'tit' (tit is a kind of bird).
'train' is an anagram indicator (I've seen 'trained' mean this (to train can mean to grow something into a shape)).
'i'+'can'='ican'
'ican' with letters rearranged gives 'anic'.
'tit'+'anic'='TITANIC'
(Other definitions for titanic that I've seen before include "Of exceptional size or power" , "Ship that sank in 1912" , "Nineteen twelve iceberg victim" , "Sinker" , "Colossal, liner" .)