Fabulous flier (3)
I believe the answer is:
roc
'fabulous flier' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for roc that I've seen before include "Gigantic bird of Arabian legend" , "Enormous legendary bird" , "Cor! what a fabulous bird" , "Mythical monstrous bird" , "Sinbad's huge bird" .)