The Collaborative International Dictionary of English v.0.48:
Fusible \Fu"si*ble\, a. [F. fusible. See Fuse, v. t.]
CapabIe of being melted or liquefied.
Fusible metal, any alloy of different metals capable of
being easily fused, especially an alloy of five parts of
bismuth, three of lead, and two of tin, which melts at a
temperature below that of boiling water. --Ure.
Fusible plug (Steam Boiler), a piece of easily fusible
alloy, placed in one of the sheets and intended to melt
and blow off the steam in case of low water.