Soften, as butter (4)
I believe the answer is:
melt
(Other definitions for melt that I've seen before include "Turn to liquid" , "Reduce from a solid to a liquid state" , "Dissolve with heat" , "Thaw" , "Become liquefied" .)
I believe the answer is:
melt
(Other definitions for melt that I've seen before include "Turn to liquid" , "Reduce from a solid to a liquid state" , "Dissolve with heat" , "Thaw" , "Become liquefied" .)