Source : Webster's Revised Unabridged Dictionary (1913)

Why \Why\, adv. [OE. whi, why, AS. hw[=i], hw?, instrumental
   case of hw[=a], hw[ae]t; akin to Icel. hv[=i] why, Dan. & Sw.
   hvi; cf. Goth. hw?. ?. See {Who}.]
   1. For what cause, reason, or purpose; on what account;
      wherefore; -- used interrogatively. See the Note under
      {What}, pron., 1.

            Turn ye, turn ye from your evil ways; for why will
            ye die, O house of Israel?            --Ezek.
                                                  xxxiii. 11.

   2. For which; on account of which; -- used relatively.

            No ground of enmity between us known Why he should
            mean me ill or seek to harm.          --Milton.

            Turn the discourse; I have a reason why I would not
            have you speak so tenderly.           --Dryden.

   3. The reason or cause for which; that on account of which;
      on what account; as, I know not why he left town so
      suddenly; -- used as a compound relative.

   Note: Why is sometimes used as an interjection or an
         expletive in expression of surprise or content at a
         turn of affairs; used also in calling. ``Why,
         Jessica!'' --Shak.

               If her chill heart I can not move, Why, I'll
               enjoy the very love.               --Cowley.
         Sometimes, also, it is used as a noun.

               The how and the why and the where. --Goldsmith.

   {For why}, because; why. See {Forwhy}. [Obs. or Colloq.]

For \For\, conj.
   1. Because; by reason that; for that; indicating, in Old
      English, the reason of anything.

            And for of long that way had walk['e]d none, The
            vault was hid with plants and bushes hoar.
                                                  --Fairfax.

            And Heaven defend your good souls, that you think I
            will your serious and great business scant, For she
            with me.                              --Shak.

   2. Since; because; introducing a reason of something before
      advanced, a cause, motive, explanation, justification, or
      the like, of an action related or a statement made. It is
      logically nearly equivalent to since, or because, but
      connects less closely, and is sometimes used as a very
      general introduction to something suggested by what has
      gone before.

            Give thanks unto the Lord; for he is good; for his
            mercy endureth forever.               --Ps. cxxxvi.
                                                  1.

            Heaven doth with us as we with torches do, Not light
            them for themselves; for if our virtues Did not go
            forth of us, 't were all alike As if we had them
            not.                                  --Shak.

   {For because}, because. [Obs.] ``Nor for because they set
      less store by their own citizens.'' --Robynson (More's
      Utopia).

   {For why}.
      (a) Why; for that reason; wherefore. [Obs.]
      (b) Because. [Obs.] See {Forwhy}.

   Syn: See {Because}.