(1):
(n.) Sounding alone.
(2):
(n.) Sounded alike in pitch; unisonant; unisonous; as, unison passages, in which two or more parts unite in coincident sound.
(3):
(n.) A single, unvaried.
(4):
(n.) Harmony; agreement; concord; union.
(5):
(n.) Identity in pitch; coincidence of sounds proceeding from an equality in the number of vibrations made in a given time by two or more sonorous bodies. Parts played or sung in octaves are also said to be in unison, or in octaves.