1. (a.) Next in order after the third; the ordinal of four.

2. (a.) Forming one of four equal parts into which anything may be divided.

3. (n.) One of four equal parts into which one whole may be divided; the quotient of a unit divided by four; one coming next in order after the third.

4. (n.) The interval of two tones and a semitone, embracing four diatonic degrees of the scale; the subdominant of any key.

consecutive intervals degree diapason diatessaron diatonic interval diatonic semitone enharmonic diesis enharmonic interval farthing fifth fourth part half step halftone interval less semitone melodic interval note octave one-fourth parallel octaves quart quarter quartern quarto second semitone seventh sixth step third tone twenty-five cents twenty-five percent two bits unison interval whole step