[with modifier] an officer in charge of a section of band instruments:a trumpet major
2 Music a major key, interval, or scale.
Bell-ringing a system of change-ringing using eight bells.
3a major organization or competition:the majors have swept up the smaller independent companies in licensing dealsit’s not unreasonable to believe someone can win all four majors [with modifier]:the oil majors had a profit bonanza
4North American a student’s principal subject or course:many students would ignore courses outside their major
[often with modifier] a student specializing in a specified subject:a math major
5 Logic a major term or premise.
6 Bridgeshort for major suit.South was anxious to mention his four-card major and bid one spade
7 Australian Rules a goal.
specialize in (a particular subject) at college or university:I was trying to decide if I should major in drama or English