major (adj.)

c. 1300, majour, "greater, more important or effective, leading, principal," from Latin maior (earlier *magios), irregular comparative of magnus "large, great" (from PIE root *meg- "great"). From 1590s as "greater in quantity, number, or extent." Used in music (of modes, scales, or chords) since 1690s, on notion of an interval a half-tone "greater" than the minor; of modern modes, "characterized by the use of major tonality throughout," by 1811. Major league, in baseball, is attested by 1892.

major (n.)

military rank above captain and below lieutenant colonel, 1640s, from French major, short for sergent-major, originally a higher rank than at present, from Medieval Latin major "chief officer, magnate, superior person," from Latin maior "an elder, adult," noun use of the adjective (see major (adj.)).

His chief duties consist in superintending the exercises of his regiment or battalion, and in putting in execution the commands of his superior officer. His ordinary position in the line is behind the left wing. [Century Dictionary, 1897]

The musical sense is attested by 1797.

major (v.)

of a college or university student, "focus (one's) studies," 1910, American English, from major (n.) in sense of "subject of specialization" (by 1890). Related: Majored; majoring. Earlier as a verb, in Scottish, "to prance about, or walk backwards and forwards with a military air and step" [Jamieson, 1825] a sense derived from the military major.

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Definitions of major
major (adj.)
of the elder of two boys with the same family name;
Jones major
major (adj.)
of greater importance or stature or rank;
a major role
major highways
a major artist
major (adj.)
greater in scope or effect;
a major contribution
a major misunderstanding
a major improvement
a major break with tradition
major (adj.)
greater in number or size or amount;
a major portion of the winnings
major (adj.)
of the field of academic study in which one concentrates or specializes;
his major field was mathematics
major (adj.)
(of a scale or mode) having half steps between the third and fourth degrees and the seventh and eighth degrees;
major scales
the key of D major
major (adj.)
of greater seriousness or danger;
a major earthquake
a major hurricane
a major illness
major (adj.)
of full legal age;
major (n.)
a commissioned military officer in the United States Army or Air Force or Marines; below lieutenant colonel and above captain;
major (n.)
a university student who is studying a particular field as the principal subject;
she is a linguistics major
major (n.)
the principal field of study of a student at a university;
her major is linguistics
major (v.)
have as one's principal field of study;
She is majoring in linguistics
Major (n.)
British statesman who was prime minister from 1990 until 1997 (born in 1943);
Synonyms: John Major / John R. Major / John Roy Major