The Collaborative International Dictionary of English v.0.48:

Believing \Be*liev"ing\, a.
   That believes; having belief. -- Be*liev"ing*ly, adv.
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The Collaborative International Dictionary of English v.0.48:

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.
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         Our conqueror (whom I now
         Of force believe almighty).              --Milton.
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         King Agrippa, believest thou the prophets ? --Acts
                                                  xxvi. 27.
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         Often followed by a dependent clause.
         I believe that Jesus Christ is the Son of God. --Acts
                                                  viii. 37.
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   Syn: See Expect.
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WordNet (r) 3.0 (2006):

believing
    n 1: the cognitive process that leads to convictions; "seeing is
         believing"