fusee
noun
fu·see fyü-ˈzē 
1
: a conical spirally grooved pulley in a timepiece from which a cord or chain unwinds onto a cylinder containing the mainspring and which by its increasing diameter compensates for the lessening power of the spring
2
: a red signal flare used especially for protecting stalled trains and trucks
Example Sentences
Recent Examples on the Web Also visible through the caseback, is the fusee-and-chain transmission, an ultra-complex and very hard-to-make solution for providing a constant force escapement that was common during this brand’s namesake founder’s heyday. 
Paige Reddinger, Robb Report, 3 Sep. 2021
Paige Reddinger, Robb Report, 3 Sep. 2021 Word History
Etymology
borrowed from French fusée "mass of thread around a spindle, explosive fuse, rocket, fusee in a timepiece," going back to Old French fusee "mass of thread around a spindle," from fus "spindle" (going back to Latin fūsus, of obscure origin) + -ee, suffix of association or containment, going back to Late Latin -āta (going back to Latin, feminine of -ātus -ate entry 3)
Note: In the later Middle Ages, French fusée designated a kind of rudimentary gunpowder-filled projectile, apparently resembling thread wound around a spindle—hence the later application to fuses, fireworks, etc.
First Known Use
1622, in the meaning defined at sense 1