Finish altering male tunic (9)
I believe the answer is:
culminate
'finish' is the definition.
(culminating is a kind of finishing)
'altering male tunic' is the wordplay.
'altering' is an anagram indicator.
'male'+'tunic'='maletunic'
'maletunic' is an anagram of 'CULMINATE'.
(Other definitions for culminate that I've seen before include "Bring to high point" , "Wind up" , "Reach a climax" , "End" , "Come to a climax (in)" .)