Actor Arnold (3)
I believe the answer is:
tom
'actor arnold' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tom that I've seen before include "Jerry's cartoon adversary" , "Edgar's Poor disguise (Lear)" , "What Dick Whittington had" , "Pig-stealing piper's son" , "Very small person" .)