late 13c., perhaps from either Old French buie or Middle Dutch boeye, both from West Germanic *baukna "beacon, signal" (see beacon). OED, however, supports Middle Dutch boeie, or Old French boie "fetter, chain" (see boy), "because of its being fettered to a spot."

late 16c., "to mark with a buoy," from buoy, n.. Meaning "rise up, lift, sustain" is from c.1600, perhaps influenced by Spanish boyar "to float," ultimately from the same source. In the figurative sense (of hopes, spirits, etc.) it is recorded from 1640s. Related: Buoyed; buoying.