The word here is probably not a noun, but the adjective "bitter."
Boost is a synonym for the word lift and starts with the letter B.
blinking
browse
Bind
beneficial
beneficial arrangement
boisterous
A synonym for "many" that starts with the letter "b" is "numerous." However, if you're looking for a word that directly starts with "b," you could consider "bountiful" as it conveys a sense of abundance.
bad, beastly
Brighter.
start or starts
brush