brain truster vs backroom boy

brain truster and backroom boy both are nouns.

Word	Noun	Adjective	Verb	Adverb
brain truster	Yes	No	No	No
backroom boy	Yes	No	No	No

As nouns, brain truster and backroom boy are synonyms defined as:

brain truster and backroom boy: an expert adviser involved in making important decisions but usually lacking official status

brain truster (noun)	backroom boy (noun)
an expert adviser involved in making important decisions but usually lacking official status	an expert adviser involved in making important decisions but usually lacking official status