The Collaborative International Dictionary of English v.0.48:

It \It\ ([i^]t), pron. [OE. it, hit, AS. hit; cf. D. het.
   [root]181. See He.]
   The neuter pronoun of the third person, corresponding to the
   masculine pronoun he and the feminine she, and having the
   same plural (they, their or theirs, them).
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   Note: The possessive form its is modern, being rarely found
         in the writings of Shakespeare and Milton, and not at
         all in the original King James's version of the Bible.
         During the transition from the regular his to the
         anomalous its, it was to some extent employed in the
         possessive without the case ending. See His, and
         He. In Dryden's time its had become quite established
         as the regular form.
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               The day present hath ever inough to do with it
               owne grief.                        --Genevan
                                                  Test.
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               Do, child, go to it grandam, child. --Shak.
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               It knighthood shall do worse. It shall fright all
               it friends with borrowing letters. --B. Jonson.
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   Note: In the course of time, the nature of the neuter sign t
         in it, the form being found in but a few words, became
         misunderstood. Instead of being looked upon as an
         affix, it passed for part of the original word. Hence
         was formed from it the anomalous genitive its,
         superseding the Saxon his. --Latham.
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               The fruit tree yielding fruit after his (its)
               kind.                              --Gen. i. 11.

   Usage: It is used,

   1. As a substance for any noun of the neuter gender; as, here
      is the book, take it home.
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   2. As a demonstrative, especially at the beginning of a
      sentence, pointing to that which is about to be stated,
      named, or mentioned, or referring to that which apparent
      or well known; as, I saw it was John.
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            It is I; be not afraid.               --Matt. xiv.
                                                  27.
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            Peter heard that it was the Lord.     --John xxi. 7.
      Often, in such cases, as a substitute for a sentence or
      clause; as, it is thought he will come; it is wrong to do
      this.
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   3. As an indefinite nominative for a impersonal verb; as, it
      snows; it rains.
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   4. As a substitute for such general terms as, the state of
      affairs, the condition of things, and the like; as, how is
      it with the sick man?
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            Think on me when it shall be well with thee. --Gen.
                                                  xl. 14.
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   5. As an indefinite object after some intransitive verbs, or
      after a substantive used humorously as a verb; as, to foot
      it (i. e., to walk).
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            The Lacedemonians, at the Straits of Thermopyl[ae],
            when their arms failed them, fought it out with
            nails and teeth.                      --Dryden.
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            Whether the charmer sinner it, or saint it,
            If folly grows romantic, I must paint it. --Pope.
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   Its self. See Itself.
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