Meaning of “major” - Learner’s Dictionary

major

adjective uk us /ˈmeɪdʒər/
IMPORTANT [ always before noun ]

B2 more important or more serious than other things or people of a similar type:

a major problem/issue
a major city
America has played a major role in the peace process.
MUSIC

in music, belonging to a key (= set of musical notes) that often produces a happy sound

→ Opposite minor adjective

(Definition of “major adjective” from the Cambridge Learner’s Dictionary © Cambridge University Press)