A rum ace, funny clown (7)
I believe the answer is:
'clown' is the definition.
(I know that Marceau has the occupation clown)
'a rum ace funny' is the wordplay.
'funny' indicates anagramming the letters.
'arumace' is an anagram of 'MARCEAU'.
(Other definitions for marceau that I've seen before include "Marcel -, French mime artist" , "famous artist speechless" , "Famous French mime artist" .)