Make one marry (5)
I believe the answer is:
unite
I believe this is a double definition.
'make one' is the first definition.
(thesaurus)
'marry' is the second definition.
(I've seen this before)
(Other definitions for unite that I've seen before include "Wed?" , "Come together as allies or comrades" , "Become an integrated whole" , "pool resources" , "old coin" .)