Worshipper vows another time (8)
I believe the answer is:
idolater
'worshipper' is the definition.
(I've seen this before)
'vows another time' is the wordplay.
'vows' becomes 'I do' (wedding vows).
'another time' becomes 'later'.
'ido'+'later'='IDOLATER'
(Other definitions for idolater that I've seen before include "I put off" , "devoted fan" , "I'm devoted to my image" , "Worshipper of false gods" , "Aaron, perhaps, in Moses' absence" .)