Fuse; dissolve (4)
I believe the answer is:
melt
I believe this clue is a double definition.
'fuse' is the first definition.
(I know that melt is a type of fuse)
'dissolve' is the second definition.
(I know that dissolve can be written as melt)
(Other definitions for melt that I've seen before include "Liquefy; become tender" , "Unfreeze" , "Go all weak" , "become soft" , "Become liquefied" .)