From Old French 'buie' (chain) or Dutch 'boeie' — a floating marker named for the chain anchoring it below.
A floating device anchored to the seabed to mark a channel, indicate a hazard, or provide a mooring point; also used as a life-saving flotation device.
From Middle English 'boie,' from Old French 'buie' (a chain, a fetter), or possibly from Middle Dutch 'boeie' (a shackle, a buoy), from Frankish *baukn (a sign, a beacon) or from Proto-Germanic *bauknaz (a beacon, a signal). An alternative etymology derives it from Old French 'buie' (chain) from Latin 'boia' (a leather collar, a fetter), from Greek 'boeiai' (ox-hide straps). The maritime sense — a floating marker anchored by a chain — may combine both the 'chain/fetter' sense (the buoy is chained to the seabed) and the 'beacon/signal' sense (the buoy
The word 'buoy' is pronounced completely differently in British and American English. The British say 'BOY' (one syllable), while Americans say 'BOO-ee' (two syllables). This is one of the most conspicuous pronunciation differences between the two varieties of English, and neither side shows any sign of yielding.