Partly from Middle Dutch boeye (“life buoy”); and partly continuing Middle French boue(e) (“a flotation signalling danger”), from Old French boue, buie (“a piece of wood or cork floating above an anchor to indicate where it is anchored”), ultimately from Frankish *baukn, from Proto-Germanic *baukną. Akin to Old High German bouhhan (“beacon”), Old Saxon bōkan (“signal”), Old Frisian bāken (“signal”), Old English bēacn (“sign, signal”).
Less likely from Latin boia (“fetter, collar”), from Ancient Greek βοείη (boeíē), (this being the feminine singular form of Ancient Greek βόειος (bóeios), see here, an adjective ('of/concerning an ox'), used substantively with an understood δορά 'hide'). More at English beacon.
bouée f (plural bouées)