Merged with foreign head employed (5)
I believe the answer is:
fused
'merged' is the definition.
('fuse' can be a synonym of 'merge')
'with foreign head employed' is the wordplay.
'with' means one lot of letters go next to another.
'head' suggests taking the first letters.
'employed' becomes 'used' ('use' can be a synonym of 'employ').
The first letter of 'foreign' is 'f'.
'f'+'used' is 'FUSED'.
(Other definitions for fused that I've seen before include "Welded together by heat" , "United" , "Equipped with safety electrical device; molten" , "Melted together" , "Coalesced" .)