Creature in frock (3)
I believe the answer is:
roc
'creature' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'in frock' is the wordplay.
'in' says the answer is hidden in the clue.
'ROC' is hidden within 'frock'.
Can you help me to learn more?
(Other definitions for roc that I've seen before include "Vast bird of legend" , "Mythical creature from Arabia" , "Sinbad's giant bird" , "Fantastic bird" , "Huge mythical bird of prey" .)