jar
Blasphemously is a long word. It begins with the letter b.
One scientific word that begins with "B" is "biology," which is the study of living organisms.
Big dipper is an outer space word. Black hole is another outer space word that begins with the letter b.
Boolean.
Baso
A 4 letter word that begins with B is bend.
belligerent
Boca Raton
Baron
But U
banimal