double bass vs contrabass

double bass and contrabass both are nouns.

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

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

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

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

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

double bass (adjective)	contrabass (adjective)
	pitched an octave below normal bass instrumental or vocal range