Blend, amalgamate (5)
I believe the answer is:
merge
This clue is a double definition.
'blend' is the first definition.
(I know that blend can be written as merge)
'amalgamate' is the second definition.
(I've seen this in another clue)
(Other definitions for merge that I've seen before include "Become combined" , "Combine into one" , "Become one" , "Amalgamate" , "Combine elements" .)