Etymology: Middle English bōst noun, bōsten verb are both found before 1300: their mutual relation and origin are unknown. (The Celtic words, Welsh bostio, Gaelic bòsd, etc., which have been hastily assumed as the source, appear to be merely adopted < English.) Various conjectures and comparisons may be seen in Wedgwood, and E. Müller, but nothing to purpose. The phonetic history of boast, showing Middle English long ō surviving as modern English long ō (oa) in northern as well as standard English, shows that boast is not < Old English *bást, which would have given northern Middle English bast, modern baist (compare ghaist, maist, Scots for ghost, most); nor < Old English *bóst, which would have given modern boost, northern buist; nor < Old English *bost, which would have retained short o (compare frost); but from a word of later (foreign) introduction. Its phonetic analogues are the Romanic words in -ost, with the o lengthened in later English, coast, roast, toast, hōst, pōst, which would lead us to expect an Old French *boster; but of this no trace has been found.

Etymology: See boast n.¹

Etymology: Of uncertain etymology: French bosse swelling, relief, as in ronde bosse ‘full relief’, has been suggested; but with little apparent fitness.

Etymology: ? < French bosse the place where the ball hits the wall. (Compare boast v.²)