Any of various instruments resembling a (large) standard guitar, but which produces lower notes; (now) especially a (usually electric) guitar with a long neck and four heavy strings tuned an octave below the lower strings on a standard guitar.
Origin
Mid 19th century.
Definition of bass guitar in US English:
bass guitar
noun
Any of various instruments resembling a (large) standard guitar, but which produces lower notes; (now) especially a (usually electric) guitar with a long neck and four heavy strings tuned an octave below the lower strings on a standard guitar.