c.1400, from L. major (earlier *magjos), irregular comp. of magnus "large, great" (see magnate). Used in music (of modes, scales, or chords) since 1694, on notion of an interval a half-tone greater than the minor. The verb meaning "focus (one's) studies" is 1924, from noun in sense of "subject of specialization" (1890).
military rank, 1643, from Fr., short for sergent-major, originally a higher rank than at present, from M.L. major "chief officer, magnate, superior person," from L. major "an elder, adult," noun use of the adjective (see major (adj.)).