Source : Webster's Revised Unabridged Dictionary (1913)

Assert \As*sert"\, v. t. [imp. & p. p. {Asserted}; p. pr. & vb.
   n. {Asserting}.] [L. assertus, p. p. of asserere to join or
   fasten to one's self, claim, maintain; ad + serere to join or
   bind together. See {Series}.]
   1. To affirm; to declare with assurance, or plainly and
      strongly; to state positively; to aver; to asseverate.

            Nothing is more shameful . . . than to assert
            anything to be done without a cause.  --Ray.

   2. To maintain; to defend. [Obs. or Archaic]

            That . . . I may assert Eternal Providence, And
            justify the ways of God to men.       --Milton.

            I will assert it from the scandal.    --Jer. Taylor.

   3. To maintain or defend, as a cause or a claim, by words or
      measures; to vindicate a claim or title to; as, to assert
      our rights and liberties.

   {To assert one's self}, to claim or vindicate one's rights or
      position; to demand recognition.

   Syn: To affirm; aver; asseverate; maintain; protest;
        pronounce; declare; vindicate.

   Usage: To {Assert}, {Affirm}, {Maintain}, {Vindicate}. To
          assert is to fasten to one's self, and hence to claim.
          It is, therefore, adversative in its nature. We assert
          our rights and privileges, or the cause of tree
          institutions, as against opposition or denial. To
          affirm is to declare as true. We assert boldly; we
          affirm positively. To maintain is to uphold, and
          insist upon with earnestness, whatever we have once
          asserted; as, to maintain one's cause, to maintain an
          argument, to maintain the ground we have taken. To
          vindicate is to use language and measures of the
          strongest kind, in defense of ourselves and those for
          whom we act. We maintain our assertions by adducing
          proofs, facts, or arguments; we are ready to vindicate
          our rights or interests by the utmost exertion of our
          powers.

Source : WordNet®

assert
     v 1: state categorically [syn: {asseverate}, {maintain}]
     2: to declare or affirm solemnly and formally as true; "Before
        God I swear I am innocent" [syn: {affirm}, {verify}, {avow},
         {aver}, {swan}, {swear}]
     3: insist on having one's opinions and rights recognized;
        "Women should assert themselves more!" [syn: {put forward}]
     4: assert to be true; "The letter asserts a free society" [syn:
         {insist}]