adviser vs backroom boy

adviser and backroom boy both are nouns.

Word	Noun	Adjective	Verb	Adverb
adviser	Yes	No	No	No
backroom boy	Yes	No	No	No

As nouns, backroom boy is a hyponym of adviser; that is, backroom boy is a word with a more specific, narrower meaning than adviser:

adviser: an expert who gives advice
backroom boy: an expert adviser involved in making important decisions but usually lacking official status

adviser (noun)	backroom boy (noun)
an expert who gives advice	an expert adviser involved in making important decisions but usually lacking official status