Bellybuttons would be the longest word I can think of beginning with a 'b' and ending in an 's'.
blitz
being
ballast
Some seven letter words starting with B are:bathtubdisturbperturbproverbrhubarbsuccumbtaxicabwashtub
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
buzzzz:)
ballast
bravery
backpack
baklava
bias
blitz
being
ballast