Crouton.
quidam, tram
bananabacteriabasilicaballerinabelugabandannabarracudabolognabulimia
Bellybuttons would be the longest word I can think of beginning with a 'b' and ending in an 's'.
Eight letter words beginning with b, ending with e:backsidebaselinebegrudgebelittleblockadeblockagebreakage
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Scarab.
Bewitch
cherrub
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I don't know the word itself as a French word, but it must be something to do with happiness (felicite, in French). The 'a' ending almost suggests an Italian word.
bath