From Middle French fusil, ultimately from Latin focus (“hearth; fire”). Doublet of fusee.
Meanings
(historical) A light flintlock musket or firelock.
[H]e out of meer wantonness attempted to trip up the heels of the soldier that stood next him, but failed in the execution, and received a blow of his breast with the butt end of a fusil, that made him stagger several paces backward. 1751, [Tobias] Smollett, The Adventures of Peregrine Pickle […], volume (please specify |volume=I to IV), London: Harrison and Co., […], →OCLC:
what might else be wrought / Fusil or grav'n in metal 1667, John Milton, “Book XI”, in Paradise Lost. […], London: […] [Samuel Simmons], and are to be sold by Peter Parker […]; [a]nd by Robert Boulter […]; [a]nd Matthias Walker, […], →OCLC; republished as Paradise Lost in Ten Books: […], London: Basil Montagu Pickering […], 1873, →OCLC:
Part of one of thoſe round Pillars that are commonly ſuppos'd to be fuſil marble: but not truly; this being of the common Suſſex Marble, full of Sea-Shells. 1728, J[ohn] Woodward, “A Catalogue of the Second Addition of English Native Fossils”, in A Catalogue of the Additional English Native Fossils, in the Collection of J. Woodward M.D., tome II, London: […] F[rancis] Fayram, […]; J[ohn] Senex, […]; and J. Osborn and T[homas] Longman, […], →OCLC, page 91:
A fusil sea. 1708, [John Philips], “Book II”, in Cyder. […], London: […] J[acob] Tonson, […], →OCLC, page 70: