javelin

Javelin comes from Middle English chafeveleyn or gavelong, borrowed from Old French javelline, a diminutive of javelot, itself a diminutive of an unattested *javel. That word traces to Vulgar Latin *gabalus, from Gaulish gabulum, from Proto-Celtic *gablā meaning 'fork' or 'forked branch', ultimately from Proto-Indo-European *gʰeh₁bʰ-.

The word passed through two rounds of diminutive suffixing in French (javelot to javelline) before settling into English, shrinking a plain word for a forked branch into the name of a slender throwing weapon.

It's cognate with gavelock and gaffle, other English words that descend from the same Old French line.