Merge or unite (7)
I believe the answer is:
combine
I believe this clue is a double definition.
'merge' is the first definition.
(I know that merge can be written as combine)
'unite' is the second definition.
(I know that unite can be written as combine)
(Other definitions for combine that I've seen before include "Mix together into one" , "Mix together different elements" , "marry" , "Put together" , "Unite, merge" .)