double bass vs bull fiddle

double bass and bull fiddle both are nouns.

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

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

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

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

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