major league

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Either of the two principal groups of professional baseball teams in the United States.
• noun A league of principal importance in other professional sports, such as basketball, football, or ice hockey.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Sports) The most important league{2} in any sport (especially baseball); contrasted with minor league. Its teams are more competent, its members are paid more, and its games attract more interest and publicity, than those of a minor league.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An association of sports teams which plays at the highest skill level of its sport, especially Major League Baseball.
• noun The highest level of competition in a field of endeavor.
• adjective Of or pertaining to a major sports league.
• adjective Analogous in importance to a major league sports team.
• adjective Serious, intensive.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the most important league in any sport (especially baseball)