Couple's welcome to church — nothing's forgotten (5)
I believe the answer is:
hitch
'couple's' is the definition.
(both can mean to join)
'welcome to church nothing's forgotten' is the wordplay.
'welcome' becomes 'hi' (both are greetings).
'church' becomes 'ch' (common abbreviation).
'nothing' becomes 'O' (looks like zero - 0).
'forgotten' suggests deleting specific letters.
'to'+'ch'='toch'
'toch' with 'o' taken away is 'tch'.
'hi'+'tch'='HITCH'
(Other definitions for hitch that I've seen before include "Yank" , "Temporary difficulty" , "Jerk" , "Unexpected problem" , "Snag; tie up (animal)" .)