Source : Webster's Revised Unabridged Dictionary (1913)

Major \Ma"jor\, [L. major, compar. of magnus great: cf. F.
   majeur. Cf. {Master}, {Mayor}, {Magnitude}, {More}, a.]
   1. Greater in number, quantity, or extent; as, the major part
      of the assembly; the major part of the revenue; the major
      part of the territory.

   2. Of greater dignity; more important. --Shak.

   3. Of full legal age. [Obs.]

   4. (Mus.) Greater by a semitone, either in interval or in
      difference of pitch from another tone.

   {Major axis} (Geom.), the greater axis. See {Focus}, n., 2.
      

   {Major key} (Mus.), a key in which one and two, two and
      three, four and five, five and six and seven, make major
      seconds, and three and four, and seven and eight, make
      minor seconds.

   {Major offense} (Law), an offense of a greater degree which
      contains a lesser offense, as murder and robbery include
      assault.

   {Major premise} (Logic), that premise of a syllogism which
      contains the major term.

   {Major scale} (Mus.), the natural diatonic scale, which has
      semitones between the third and fourth, and seventh and
      fourth, and seventh and eighth degrees; the scale of the
      major mode, of which the third is major. See {Scale}, and
      {Diatonic}.

   {Major second} (Mus.), a second between whose tones is a
      difference in pitch of a step.

   {Major sixth} (Mus.), a sixth of four steps and a half step.
      In major keys the third and sixth from the key tone are
      major. Major keys and intervals, as distinguished from
      minors, are more cheerful.

   {Major term} (Logic), that term of a syllogism which forms
      the predicate of the conclusion.

   {Major third} (Mus.), a third of two steps.

Major \Ma"jor\, n. [F. major. See {Major}, a.]
   1. (Mil.) An officer next in rank above a captain and next
      below a lieutenant colonel; the lowest field officer.

   2. (Law) A person of full age.

   3. (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].

   Note: In hypothetical syllogisms, the hypothetical premise is
         called the major.

   4. [LL. See {Major}.] A mayor. [Obs.] --Bacon.

Source : WordNet®

major
     adj 1: of greater importance or stature or rank; "a major artist";
            "a major role"; "major highways" [ant: {minor}]
     2: greater in scope or effect; "a major contribution"; "a major
        improvement"; "a major break with tradition"; "a major
        misunderstanding" [ant: {minor}]
     3: greater in number or size or amount; "a major portion (a
        majority) of the population"; "Ursa Major"; "a major
        portion of the winnings" [ant: {minor}]
     4: of the field of academic study in which one concentrates or
        specializes; "his major field was mathematics" [ant: {minor}]
     5: of a scale or mode; "major scales"; "the key of D major"
        [ant: {minor}]
     6: of greater seriousness or danger; "a major earthquake"; "a
        major hurricane"; "a major illness" [ant: {minor}]
     7: of full legal age; "major children" [ant: {minor}]
     8: of the elder of two boys with the same family name; "Jones
        major" [syn: {major(ip)}]

major
     n 1: a commissioned military officer in the United States Army or
          Air Force or Marines; below lieutenant colonel and above
          captain
     2: British statesman who was prime minister from 1990 until
        1997 (born in 1943) [syn: {John Major}, {John R. Major}, {John
        Roy Major}]
     3: a university student who is studying a particular field as
        the principal subject; "she is a linguistics major"
     4: the principal field of study of a student at a university;
        "her major is linguistics"

major
     v : have as one's principal field of study; "She is majoring in
         linguistics"