Synonyms for Contrabass (same or very similar meaning)
WordNet sense 1 (largest and lowest member of the violin family):
bass fiddle, bass viol, bull fiddle, double bass, string bassWordNet sense 2 (pitched an octave below normal bass instrumental or vocal range):
double-bassWordNet sense 3 (used of sounds and voices; low in pitch or frequency):
low, low-pitchedFrom the ODE community, based on WordNetadd/edit