Tread the boards (3)
I believe the answer is:
act
'tread the boards' is the definition.
(to 'tread the boards' is to act on stage)
This is all the clue.
(Other definitions for act that I've seen before include "Produce an effect" , "Parliamentary decree" , "Pretend to be - deed" , "Perform theatrically" , "Subdivision of a play" .)