Hat put back on after end of Mass (7)
I believe the answer is:
stetson
'hat' is the definition.
(Stetson is an example)
'put back on after end of mass' is the wordplay.
'put back' becomes 'stet' (I've seen this in other clues).
'after' is a charade indicator (letters next to each other).
'end of' says to take the final letters.
The last letter of 'mass' is 's'.
'on' after 's' is 'son'.
'stet'+'son'='STETSON'
(Other definitions for stetson that I've seen before include "capital item" , "Hat for country-and-western singers, Texan oil magnates, etc." , "Tip" , "Large hat" , "Ten-gallon hat" .)