Source : Webster's Revised Unabridged Dictionary (1913)

Believe \Be*lieve"\, v. t. [imp. & p. p. {Believed}; p. pr. &
   vb. n. {Believing}.] [OE. bileven (with pref. be- for AS.
   ge-), fr. AS. gel?fan, gel?fan; akin to D. gelooven, OHG.
   gilouban, G. glauben, OS. gil?bian, Goth. galaubjan, and
   Goth. liubs dear. See {Lief}, a., {Leave}, n.]
   To exercise belief in; to credit upon the authority or
   testimony of another; to be persuaded of the truth of, upon
   evidence furnished by reasons, arguments, and deductions of
   the mind, or by circumstances other than personal knowledge;
   to regard or accept as true; to place confidence in; to
   think; to consider; as, to believe a person, a statement, or
   a doctrine.

         Our conqueror (whom I now Of force believe almighty).
                                                  --Milton.

         King Agrippa, believest thou the prophets ? --Acts
                                                  xxvi. 27.

         Often followed by a dependent clause. I believe that
         Jesus Christ is the Son of God.          --Acts viii.
                                                  37.

   Syn: See {Expect}.

Believing \Be*liev"ing\, a.
   That believes; having belief. -- {Be*liev"ing*ly}, adv.

Source : WordNet®

believing
     n : the cognitive process that leads to convictions; "seeing is
         believing"