Mostly ineffective, church magazine in the past (5)
I believe the answer is:
punch
'magazine in the past' is the definition.
'mostly ineffective church' is the wordplay.
'mostly' means to remove the last letter.
'ineffective' becomes 'puny'.
'church' becomes 'ch' (common abbreviation).
'puny' with its last letter taken off is 'pun'.
'pun'+'ch'='PUNCH'
(Other definitions for punch that I've seen before include "that would be attached to haywain for pulling?" , "Drink - attack" , "horse to get > drink" , "Seaside puppet character" , "Blow with the fist" .)