(from the Latin word dominari, to rule or govern), among musicians, is used either as an adjective or substantive; but these different acceptations are far from being indiscriminate. In both senses it is explained by Rousseau. The dominant or sensible chord is that which is practised upon the dominant of the tone, and which introduces a perfect cadence. Every perfect major chord becomes a dominant chord as soon as the seventh minor is added to it.

Dominant (substantive). Of the three notes essential to the tone, it is that which is a fifth from the tonic. The tonic and the dominant fix the tone, in which they are each of them the fundamental sound of a particular chord; whereas the mediant, which constitutes the mode, has no chord peculiar to itself, and only makes a part of the chord of the tonic.

Rameau gives the general name of dominant to every note which carries a chord of the seventh, and distinguishes that which carries the sensible chord by the name of a tonic dominant; but on account of the length of the word, this addition to the name has not been adopted by musicians, who continue simply to call that note a dominant which is a fifth from the tonic; and they do not call the other notes which carry a fifth of the seventh dominants, but fundamentals, which is sufficient to render their meaning plain, and to prevent confusion.

A dominant, in that species of church music which is called plain-chant, is that note which is most frequently repeated or beaten, in whatever degree it may be from the tonic. In this species of music there are dominants and tonics, but no mediant.