Intervals are those in which the two tones have no mathematical relationship. (Opposite of "consonant"). Dissonant intervals are though to be harsh or somewhat disturbing, and need to be resolved.
The absence of consonance characterized by a rough sound resulting from the beats produced by two or more tones whose frequencies do not relate.
dischordant. sounds like the notes do not belong together.
Unpleasant to the ear; ugly-sounding. Dissonance is an imperfection only when the music is not supposed to sound dissonant. Compare "consonant."