'Fusible plug' definitions:

Definition of 'Fusible plug'

From: GCIDE

Fusible \Fu"si*ble\, a. [F. fusible. See Fuse, v. t.] CapabIe of being melted or liquefied. [1913 Webster]
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. [1913 Webster]