bass fiddle vs string bass

bass fiddle and string bass both are nouns.

Word	Noun	Adjective	Verb	Adverb
bass fiddle	Yes	No	No	No
string bass	Yes	No	No	No

As nouns, bass fiddle and string bass are synonyms defined as:

bass fiddle and string bass: largest and lowest member of the violin family

Other synonyms of bass fiddle include bass viol, bull fiddle, contrabass, double bass.

bass fiddle (noun)	string bass (noun)
largest and lowest member of the violin family	largest and lowest member of the violin family