The Collaborative International Dictionary of English v.0.48:

Will \Will\, n. [OE. wille, AS. willa; akin to OFries. willa,
   OS. willeo, willio, D. wil, G. wille, Icel. vili, Dan.
   villie, Sw. vilja, Goth wilja. See Will, v.]
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   1. The power of choosing; the faculty or endowment of the
      soul by which it is capable of choosing; the faculty or
      power of the mind by which we decide to do or not to do;
      the power or faculty of preferring or selecting one of two
      or more objects.
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            It is necessary to form a distinct notion of what is
            meant by the word "volition" in order to understand
            the import of the word will, for this last word
            expresses the power of mind of which "volition" is
            the act.                              --Stewart.
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            Will is an ambiguous word, being sometimes put for
            the faculty of willing; sometimes for the act of
            that faculty, besides [having] other meanings. But
            "volition" always signifies the act of willing, and
            nothing else.                         --Reid.
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            Appetite is the will's solicitor, and the will is
            appetite's controller; what we covet according to
            the one, by the other we often reject. --Hooker.
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            The will is plainly that by which the mind chooses
            anything.                             --J. Edwards.
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   2. The choice which is made; a determination or preference
      which results from the act or exercise of the power of
      choice; a volition.
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            The word "will," however, is not always used in this
            its proper acceptation, but is frequently
            substituted for "volition", as when I say that my
            hand mover in obedience to my will.   --Stewart.
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   3. The choice or determination of one who has authority; a
      decree; a command; discretionary pleasure.
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            Thy will be done.                     --Matt. vi.
                                                  10.
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            Our prayers should be according to the will of God.
                                                  --Law.
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   4. Strong wish or inclination; desire; purpose.
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   Note: "Inclination is another word with which will is
         frequently confounded. Thus, when the apothecary says,
         in Romeo and Juliet,
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               My poverty, but not my will, consents; . . .
               Put this in any liquid thing you will,
               And drink it off.
         [1913 Webster] the word will is plainly used as,
         synonymous with inclination; not in the strict logical
         sense, as the immediate antecedent of action. It is
         with the same latitude that the word is used in common
         conversation, when we speak of doing a thing which duty
         prescribes, against one's own will; or when we speak of
         doing a thing willingly or unwillingly." --Stewart.
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   5. That which is strongly wished or desired.
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            What's your will, good friar?         --Shak.
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            The mariner hath his will.            --Coleridge.
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   6. Arbitrary disposal; power to control, dispose, or
      determine.
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            Deliver me not over unto the will of mine enemies.
                                                  --Ps. xxvii.
                                                  12.
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   7. (Law) The legal declaration of a person's mind as to the
      manner in which he would have his property or estate
      disposed of after his death; the written instrument,
      legally executed, by which a man makes disposition of his
      estate, to take effect after his death; testament; devise.
      See the Note under Testament, 1.
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   Note: Wills are written or nuncupative, that is, oral. See
         Nuncupative will, under Nuncupative.
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   At will (Law), at pleasure. To hold an estate at the will
      of another, is to enjoy the possession at his pleasure,
      and be liable to be ousted at any time by the lessor or
      proprietor. An estate at will is at the will of both
      parties.

   Good will. See under Good.

   Ill will, enmity; unfriendliness; malevolence.

   To have one's will, to obtain what is desired; to do what
      one pleases.

   Will worship, worship according to the dictates of the will
      or fancy; formal worship. [Obs.]

   Will worshiper, one who offers will worship. [Obs.] --Jer.
      Taylor.

   With a will, with willingness and zeal; with all one's
      heart or strength; earnestly; heartily.
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WordNet (r) 3.0 (2006):

at will
    adv 1: as one chooses or pleases; "he can roam the neighborhood
           at will"