What is the meaning of the word "major"?

Definitions:

a university student who is studying a particular field as the principal subject noun
- I am a major in liguistics.
greater in number or size or amount adjective
- a major portion (a majority) of the population
greater in scope or effect adjective
- a major contribution
have as one's principal field of study verb
- They are majoring in linguistics at a school known for those studies.
of a scale or mode adjective
- major scales
of greater importance or stature or rank adjective
- a major artist
of greater seriousness or danger adjective
- a major earthquake
of the field of academic study in which one concentrates or specializes adjective
- My major field was mathematics.
the principal field of study of a student at a university noun
- My major is linguistics.