Couple row endlessly (3)
I believe the answer is:
tie
'couple' is the definition.
(both can mean to join)
'row endlessly' is the wordplay.
'row' becomes 'tier' (a tier is a row of things).
'endlessly' means to remove the last letter.
'tier' with its final letter taken off is 'TIE'.
(Other definitions for tie that I've seen before include "hamper" , "Knot; link" , "Knot; achieve the same score" , "Stalemate" , "garb" .)