major

1 adjective

1 (usually before noun) very large or important, when compared to other things or people of a similar kind: There are two major political parties in the US. | Mahler's music was a major influence on the young composer. | one of the major causes of cancer

—opposite minor 1 (1)

2 (usually before noun) having very serious or worrying results: The loss of Cantona through injury was a major setback for the team. | major problem: This could create major traffic problems.

3 (not before noun) AmE spoken very important: This is major? You got me out of bed for this?

4 a major key (key1 (4)) is based on a musical scale in which there are semitones between the third and fourth and the seventh and eighth notes: a symphony in D major

—compare minor 1 (2) 2 noun (C)

1 an officer of middle rank in the British or US army or marines, or in the US airforce

—see also: drum major

2 especially AmE the main subject that a student studies at college or university: Her major is history.

—compare minor 2 (2)

3 AmE someone studying a particular subject as their main subject at college or university: She's a history major.

4 the majors (plural) the Major Leagues

—compare minor league 3 verb major in sth phrasal verb (T) especially AmE to study something as your main subject at college or university: He's majoring in Political Science.