Next after the third: an ordinal numeral.n. The quotient of unity divided by four; one of four equal parts of anything; a quarter: as, three fourths (¾) of an acre.n. In early English law, a fourth part of the rents of the year, or of movables, or both, granted or levied by way of tax.n. In music A tone four diatonic degrees above or below any given tone.n. The interval between any tone and a tone four degrees distant from it.n. The harmonic combination of two such tones.n. In a scale, the fourth tone from the bottom; the subdominant: solmizated fa, as F in the scale of C, or D in that of A.