Source : Webster's Revised Unabridged Dictionary (1913)

Maintain \Main*tain\, v. t. [imp. & p. p. {Maintained}; p. pr. &
   vb. n. {Maintaining}.] [OE. maintenen, F. maintenir,
   properly, to hold by the hand; main hand (L. manus) + F.
   tenir to hold (L. tenere). See {Manual}, and Tenable.]
   1. To hold or keep in any particular state or condition; to
      support; to sustain; to uphold; to keep up; not to suffer
      to fail or decline; as, to maintain a certain degree of
      heat in a furnace; to maintain a fence or a railroad; to
      maintain the digestive process or powers of the stomach;
      to maintain the fertility of soil; to maintain present
      reputation.

   2. To keep possession of; to hold and defend; not to
      surrender or relinquish.

            God values . . . every one as he maintains his post.
                                                  --Grew.

   3. To continue; not to suffer to cease or fail.

            Maintain talk with the duke.          --Shak.

   4. To bear the expense of; to support; to keep up; to supply
      with what is needed.

            Glad, by his labor, to maintain his life.
                                                  --Stirling.

            What maintains one vice would bring up two children.
                                                  --Franklin.

   5. To affirm; to support or defend by argument.

            It is hard to maintain the truth, but much harder to
            be maintained by it.                  --South.

   Syn: To assert; vindicate; allege. See {Assert}.

Source : WordNet®

maintain
     v 1: keep in a certain state, position, or activity; e.g., "keep
          clean"; "hold in place"; "She always held herself as a
          lady"; "The students keep me on my toes" [syn: {keep}, {hold}]
     2: keep in safety and protect from harm, decay, loss, or
        destruction; "We preserve these archeological findings";
        "The old lady could not keep up the building"; "children
        must be taught to conserve our national heritage"; "The
        museum curator conserved the ancient manuscripts" [syn: {conserve},
         {preserve}, {keep up}]
     3: supply with necessities and support; "She alone sustained
        her family"; "The money will sustain our good cause";
        "There's little to earn and many to keep" [syn: {sustain},
         {keep}]
     4: state categorically [syn: {assert}, {asseverate}]
     5: of power or authority [syn: {wield}, {exert}]
     6: maintain for use and service; "I keep a car in the
        countryside"; "She keeps an apartment in Paris for her
        shopping trips" [syn: {keep}]
     7: maintain by writing regular records; "keep a diary";
        "maintain a record"; "keep notes" [syn: {keep}]
     8: state or assert; "He maintained his innocence" [syn: {defend}]
     9: support against an opponent; "The appellate court upheld the
        verdict" [syn: {uphold}]
     10: observe correctly or closely; "The pianist kept time with
         the metronome"; "keep count"; "I cannot keep track of all
         my employees" [syn: {observe}, {keep}]