Theatrical Frenchman in beret (4)
I believe the answer is:
camp
'theatrical' is the definition.
(I've seen this before)
'frenchman in beret' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'in' means one lot of letters goes inside another.
'beret' becomes 'cap' (I've seen this in another clue).
'm' put into 'cap' is 'CAMP'.
(Other definitions for camp that I've seen before include "Bivouac, group of tents" , "Where guys are tense" , "Affected in mannerisms" , "Tent site" , "Effeminate; military base" .)