ETYM Latin dissonantia: cf. French dissonance.
Two or more sounds that, when heard together, sound unpleasant.
In music, a combination of two or more tones displeasing to the ear. It is the opposite of a consonance, and is judged dissonant by the presence of a beat frequency.
Equal temperament involves a measure of deliberate distuning of intervals to allow free modulation between keys. On the harpsichord and piano, the effect is disguised by making unison strings (courses) internally dissonant, an effect also improving tonal sustain.