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1680s, "to melt" (transitive), back-formation from fusion. Intransitive sense, "to become liquid," attested from 1800. Figurative sense of "blend different things" is first recorded 1817. Related: Fused; fusing.
"combustible cord or tube for lighting an explosive device," also fuze, 1640s, from Italian fuso "spindle" (so called because the originals were long, thin tubes filled with gunpowder), from Latin fusus "spindle," of uncertain origin. Influenced by French fusée "spindleful of hemp fiber," and obsolete English fusee "musket fired by a fuse." Meaning "device that breaks an electrical circuit" first recorded 1884, so named for its shape, but erroneously attributed to fuse (v.) because it melts.