bass fiddle vs double bass

bass fiddle and double bass both are nouns.

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

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

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

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

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