One of five in a Shakespeare play (3)
I believe the answer is:
act
'one of five in a shakespeare play' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for act that I've seen before include "Function" , "Aussie parliamentarians exert influence here?" , "performing group" , "Feat" , "Subdivision of a play" .)