Join together; make one (5)
I believe the answer is:
unite
I believe this clue is a double definition.
'join together' is the first definition.
(I've seen this in another clue)
'make one' is the second definition.
(I've seen this in another clue)
(Other definitions for unite that I've seen before include "fuse" , "Pull together" , "Amalgamate" , "Become an integrated whole" , "Put together" .)