Definitions
1.nounAn association of sports teams which plays at the highest skill level of its sport, especially Major League Baseball.
2.noun(usually in plural or attributive) The highest level of competition in a field of endeavor."You can't be so casual. You're in the major leagues now."
3.adjectiveOf or pertaining to a major sports league; belonging to the professional level of a sport, such as US baseball.
4.adjectiveAnalogous in importance to a major league sports team."Calatrava is a major league architect."
5.adjectiveSerious, high-level; significant"Bill accidentally faxed sensitive documents to our competitors, and such a major league mess-up could only be dealt with by firing Bill."