Emily Dickinson Lexicon

DOM'IN-ANT, a. [L. dominans, from dominor, to rule; dominus, lord, master; either from domus, a house, or from domo, δαμαω, to overcome, to tame, to subdue, W. dovi. Both roots unite in the sense, to set, to press, to fix. See Class Dm, No. 1, 3.]

1. Ruling; prevailing; governing; predominant; as, the dominant party or faction. Reid. Tooke.
2. In music, the dominant or sensible chord is that which is practiced on 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. – Rousseau. Encyc.