major

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

• adjective Greater than others in importance or rank.
• adjective Great in scope or effect.
• adjective Great in number, size, or extent.
• adjective Requiring great attention or concern; very serious.
• adjective Law Legally recognized as having reached the age of adulthood.
• adjective Of or relating to the field of academic study in which a student specializes.
• adjective Designating a scale or mode having half steps between the third and fourth and the seventh and eighth degrees.
• adjective Equivalent to the distance between the tonic note and the second or third or sixth or seventh degrees of a major scale or mode.
• adjective Based on a major scale.
• noun A commissioned rank in the US Army, Air Force, or Marine Corps that is above captain and below lieutenant colonel.
• noun One who holds this rank.
• noun One that is superior in rank, importance, or ability.
• noun Law One recognized by the law as having reached the age of adulthood.
• noun A field of study chosen as an academic specialty.
• noun A student specializing in such studies.
• noun A major premise.
• noun A major term.
• noun A major scale, key, interval, or mode.
• noun A chord containing a major third between the first and second notes and a minor third between the second and third notes.
• noun Sports The major leagues.
• intransitive verb To pursue academic studies in a major.

from The Century Dictionary.

• To act the major; look and talk big, or with a military air.
• In prosody, noting the longer of two types of verse which bear a common name.
• Greater; more important or effective; first in force or consideration; leading; principal: as, the major premise or term of a syllogism.
• Greater in quantity, number, or extent: as, the major part of the revenue, of an assembly, or of a territory.
• Of age; having attained to majority.
• In music
• Of intervals, standard or normal; literally “greater,” as compared with minor intervals.
• Of tones, distant by a major interval from a given tone: as, A is the major third of F, etc.
• Of tonalities and scales, standard or normal: characterized by a major third and also by a major sixth and seventh: opposed to minor.
• Of triads and chords, characterized by a major third between the root and the tone next above, and a perfect fifth between the root and the second tone above: opposed to minor, diminished, and augmented.
• Of cadences, ending in a major triad.
• Of modes in the modern sense, and thus of composition in general, characterized by the use of a major tonality and of major cadences: as, a piece is written throughout in the major mode.
• In logic, wider; broader; more extensive; a predicate to more subjects.
• noun Milit., an officer next in rank above a captain and below a lieutenant-colonel; the lowest field-officer.
• noun In law, a person who is old enough to manage his own concerns. See age, n., 3.
• noun In music, the major mode, or a major tonality or major chord, taken absolutely.
• noun In logic
• noun The major premise of a syllogism, which in direct syllogisms states the rule from which the conclusion is drawn.
• noun The major extreme of a syllogism.
• noun Same as mayor.

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

• noun (Mil.) An officer next in rank above a captain and next below a lieutenant colonel; the lowest field officer.
• noun (Law) A person of full age.
• noun (Logic) That premise which contains the major term. It its the first proposition of a regular syllogism; as: No unholy person is qualified for happiness in heaven [the major]. Every man in his natural state is unholy [minor]. Therefore, no man in his natural state is qualified for happiness in heaven [conclusion or inference].
• noun obsolete A mayor.