Coalesce; melt (4)
I believe the answer is:
fuse
I believe this is a double definition.
'coalesce' is the first definition.
(I know that coalesce can be written as fuse)
'melt' is the second definition.
(I know that fuse is a type of melt)
(Other definitions for fuse that I've seen before include "Join, coalesce" , "Tube or cord for igniting an explosive" , "Electrical fitting" , "Melt with heat" , "Common electrical safety device in homes etc" .)