Three or more tones sounding simultaneously. In traditional European music
the
base chord is a
triad consisting of 2
thirds.
Major (major
+
minor
third) as well as
minor (minor + major third)
chords may be extended with more thirds. Four-tone
seventh chords and five-tone
ninth major chords are most often used as dominants
(
functional harmony). A special case is chords having no
third above the lower notes to define their quality as major or minor. Such
chords are denoted open chords
Music Dictionary