Source : Webster's Revised Unabridged Dictionary (1913)

Assure \As*sure\, v. t. [imp. & p. p. {Assured}; p. pr. & vb. n.
   {Assuring}.] [OF. ase["u]rer, F. assurer, LL. assecurare; L.
   ad + securus secure, sure, certain. See {Secure}, {Sure}, and
   cf. {Insure}.]
   1. To make sure or certain; to render confident by a promise,
      declaration, or other evidence.

            His promise that thy seed shall bruise our foe . . .
            Assures me that the bitterness of death Is past, and
            we shall live.                        --Milton.

   2. To declare to, solemnly; to assert to (any one) with the
      design of inspiring belief or confidence.

            I dare assure thee that no enemy Shall ever take
            alive the noble Brutus.               --Shak.

   3. To confirm; to make certain or secure.

            And it shall be assured to him.       --Lev. xxvii.
                                                  19.

            And hereby we know that we are of the truth, and
            shall assure our hearts before him.   --1 John iii.
                                                  19.

   4. To affiance; to betroth. [Obs.] --Shak.

   5. (Law) To insure; to covenant to indemnify for loss, or to
      pay a specified sum at death. See {Insure}.

   Syn: To declare; aver; avouch; vouch; assert; asseverate;
        protest; persuade; convince.

Source : WordNet®

assure
     v 1: make certain of; "This nest egg will ensure a nice
          retirement for us"; "Preparation will guarantee
          success!" [syn: {guarantee}, {ensure}, {insure}, {secure}]
     2: inform positively and with certainty and confidence; "I tell
        you that man is a crook!" [syn: {tell}]
     3: assure somebody of the truth of something with the intention
        of giving the listener confidence; "I assured him that
        traveling to Cambodia was safe"
     4: be careful or certain to do something; make certain of
        something; "He verified that the valves were closed"; "See
        that the curtains are closed"; "control the quality of the
        product" [syn: {see}, {check}, {insure}, {see to it}, {ensure},
         {control}, {ascertain}]
     5: cause to feel sure; give reassurance to; "The airline tried
        to reassure the customers that the planes were safe" [syn:
         {reassure}] [ant: {worry}]
     6: make a promise or commitment [syn: {promise}]