Definition of "fusible"

Although a fusible plug is provided in the firebox crown of every locomotive, so that by melting if the inner firebox crown becomes uncovered, and thereby releasing steam at full pressure into the firebox, the fire may be extinguished and the crew given an unmistakable warning of the danger, there is no absolute guarantee that the plug will melt.

1941 March, “The Why and the Wherefore: Burst Boilers”, in Railway Magazine, page 143

Try any fusibles you have on hand, making sure that they aren't too stiff for the project you have in mind.

2010, Susan Stein, The Complete Photo Guide to Textile Art, page 40