Nouns are not describing words. The words that describe nouns are adjectives. A synonym is a noun for another noun.
Some nouns that are synonyms for girl that start with B are:
bride
beauty
baby
Basketball player
ballerina
baker
Something that is used to stay warm that starts with the letter B could be a blanket.
barley
baseball game
boat
Ballet
brenda
The word here is probably not a noun, but the adjective "bitter."
Bear starts with the letter B
The chicken that starts with B is bantam.
Belgium is a country that starts with B.
a BMW starts with the letter b!!
A bumper sticker is sticky. It starts with the letter b.
Baclofen is a muscle relaxer that starts with the letter B
The word 'boom' can be used as a word for explosion that starts with a b.
unuseless
Boost is a synonym for the word lift and starts with the letter B.
No country that borders Libya starts with the letter B.