Reptile caught by fabulous flying creature (4)
I believe the answer is:
croc
'reptile' is the definition.
(I've seen this before)
'caught by fabulous flying creature' is the wordplay.
'caught' becomes 'c' (cricket abbreviation).
'by' is a charade indicator (letters next to each other).
'fabulous flying creature' becomes 'roc' (mythical bird).
'c'+'roc'='CROC'
(Other definitions for croc that I've seen before include "Small reptile" , "Fierce beast" , "Pot tailless" , "Predatory reptile (informal)" , "creature heard to be a vicious one" .)