Mediant \Me"di*ant\, n. [L. medians, p. p. of mediare to halve: cf. It. mediante, F. m['e]diante.] (Mus.) The third above the keynote; -- so called because it divides the interval between the tonic and dominant into two thirds.
mediant n : (music) the third note of a diatonic scale; midway between the tonic and the dominant