The Collaborative International Dictionary of English v.0.48:

Wherefore \Where"fore\, adv. & conj. [Where + for.]
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   1. For which reason; so; -- used relatively.
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            Wherefore by their fruits ye shall know them.
                                                  --Matt. vii.
                                                  20.
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   2. For what reason; why; -- used interrogatively.
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            But wherefore that I tell my tale.    --Chaucer.
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            Wherefore didst thou doubt?           --Matt. xiv.
                                                  31.
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The Collaborative International Dictionary of English v.0.48:

Wherefore \Where"fore\, n.
   the reason why. [Colloq.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

wherefore
    n 1: the cause or intention underlying an action or situation,
         especially in the phrase `the whys and wherefores' [syn:
         why, wherefore]