<p><strong>Noun</strong></p><ul><li>coincidence in pitch of two or more musical tones, voices, etc.</li><li>the musical interval of a perfect prime.</li><li>the performance of musical parts at the same pitch or at the octave.</li><li>a sounding together in octaves, especially of male and female voices or of higher and lower instruments of the same class.</li><li>a process in which all elements behave in the same way at the same time; simultaneous or synchronous parallel action: to march in unison.</li></ul>