\U"ni*son\ (?; 277), n. [LL. unisonus having the same
sound; L. unus one + sonus a sound: cf. F. unisson, It.
unisono. See {One}, and {Sound} a noise.]
1. Harmony; agreement; concord; union.
2. (Mus.) 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.
Note: If two cords of the same substance have equal length,
      thickness, and tension, they are said to be in unison,
      and their sounds will be in unison. Sounds of very
      different qualities and force may be in unison, as the
      sound of a bell may be in unison with a sound of a
      flute. Unison, then, consists in identity of pitch
      alone, irrespective of quality of sound, or timbre,
      whether of instruments or of human voices. A piece or
      passage is said to be sung or played in unison when all
      the voices or instruments perform the same part, in
      which sense unison is contradistinguished from harmony.
3. A single, unvaried. [R.] --Pope.
{In unison}, in agreement; agreeing in tone; in concord.

\U"ni*son\ (?; 277), a. [Cf. It. unisono. See {Unison},
n.]
1. Sounding alone. [Obs.]
         [sounds] intermixed with voice, Choral or unison.
                                               --Milton.
2. (Mus.) Sounded alike in pitch; unisonant; unisonous; as,
   unison passages, in which two or more parts unite in
   coincident sound.