Do something - take part! (3)
I believe the answer is:
act
I believe this clue is a triple definition!
'do something' is the first definition.
(to act is to do something)
'take' is the second definition.
(thesaurus)
'part' is the third definition.
(I have seen 'Part of play ' mean 'act' so perhaps 'part' could also mean 'act')
(Other definitions for act that I've seen before include "Play (a role)" , "Accomplishment" , "Parliamentary decree" , "Do something (on stage?)" , "Perform on stage" .)