Pronunciation: [fjˈuːsiː] (IPA) 
The word "fusee" is often misspelled as "fusée" due to the French origin of the word. However, the correct spelling for this word is "fusee" without the accent. The word refers to a flared tube used in early firearm technology or a safety device inserted in some clocks and mechanical engines. It is pronounced as /fyoo-zee/, with the emphasis on the first syllable /fyoo/ and a silent "e" at the end.
A fusee, also spelled fusée, is a small conical device primarily used in mechanical timepieces, such as mechanical watches and clocks, to regulate the speed and accuracy of the watch movement. Essentially, it is a spiral-shaped chain that is wound around a cone-shaped barrel inside the timepiece.
The purpose of a fusee is to ensure a consistent and reliable power output to the watch or clock. As the mainspring inside the barrel unwinds, the fusee gradually releases the tension in a controlled manner by shifting the point of contact on the spiral chain. This action compensates for the variable force exerted by the mainspring, which naturally weakens as it unwinds, thereby maintaining an even power flow to the mechanism.
By using the fusee, watchmakers can accomplish a more consistent power output throughout the duration of the watch's winding. This helps to optimize the accuracy and longevity of the timepiece, as it compensates for the diminishing force of the mainspring.
Historically, fusees were widely used in early timekeeping devices and can be traced back to the 15th century. Although modern watchmaking techniques have made fusees less common today, they still remain highly revered in the horological world for their intricate engineering and contribution to timekeeping accuracy.
• A tube filled with a combustible composition, used for firing shells or for blasting.
• A match; a cigar-light.
• The cone or conical part of a watch or clock round which the chain is wound.
Etymological and pronouncing dictionary of the English language. By Stormonth, James, Phelp, P. H. Published 1874.
The word "fusee" originated from the French word "fusée", which means "spindle" or "rocket". It is derived from the Latin word "fūsus", which means "spindle". In the context of timekeeping, "fusee" refers to a cone-shaped pulley used in mechanical watches and clocks to ensure a constant power flow, preventing the mainspring from unwinding too quickly and maintaining a consistent force to power the timepiece. The term "fusee" was first used in English in the 17th century when referring to this specific mechanism.
