1680s, "to melt, make liquid by heat" (transitive), back-formation from fusion. Intransitive sense, "to become liquid," attested from 1800. Figurative sense of "blend different things, blend or unite as if by melting together" is recorded by 1817. Intransitive figurative sense "become intermingled or blended" is by 1873. Related: Fused; fusing.

"combustible cord or tube for lighting an explosive device," also fuze, 1640s, from Italian fuso, literally "spindle" (the ignition device so called for its shape, because the originals were long, thin tubes filled with gunpowder), from Latin fusus "a spindle," which is of uncertain origin. Influenced by French cognate fusée "spindleful of hemp fiber," and obsolete English fusee "musket fired by a fuse," which is from French. Meaning "device that breaks an electrical circuit" is first recorded 1884, so named for its shape, but erroneously attributed to fuse (v.) because it melts.