Source : Webster's Revised Unabridged Dictionary (1913)

Who \Who\, pron. [Possess. {whose}; object. {Whom}.] [OE. who,
   wha, AS. hw[=a], interrogative pron., neut. hw[ae]t; akin to
   OFries. hwa, neut. hwet, OS. hw[=e], neut. hwat, D. wie,
   neut. wat, G. wer, neut. was, OHG. wer, hwer, neut. waz,
   hwaz, Icel. hvat, neut., Dan. hvo, neut. hvad, Sw. ho, hvem,
   neut. hvad, Goth. hwas, fem. hw[=o], neut. hwa, Lith. kas,
   Ir. & Gael. co, W. pwy, L. quod, neuter of qui, Gr. po`teros
   whether, Skr. kas. [root]182. Cf. {How}, {Quantity},
   {Quorum}, {Quote}, {Ubiquity}, {What}, {When}, {Where},
   {Whether}, {Which}, {Whither}, {Whom}, {Why}.]
   1. Originally, an interrogative pronoun, later, a relative
      pronoun also; -- used always substantively, and either as
      singular or plural. See the Note under {What}, pron., 1.
      As interrogative pronouns, who and whom ask the question:
      What or which person or persons? Who and whom, as relative
      pronouns (in the sense of that), are properly used of
      persons (corresponding to which, as applied to things),
      but are sometimes, less properly and now rarely, used of
      animals, plants, etc. Who and whom, as compound relatives,
      are also used especially of persons, meaning the person
      that; the persons that; the one that; whosoever. ``Let who
      will be President.'' --Macaulay.

            [He] should not tell whose children they were.
                                                  --Chaucer.

            There thou tell'st of kings, and who aspire; Who
            fall, who rise, who triumph, who do moan. --Daniel.

            Adders who with cloven tongues Do hiss into madness.
                                                  --Shak.

            Whom I could pity thus forlorn.       --Milton.

            How hard is our fate, who serve in the state.
                                                  --Addison.

            Who cheapens life, abates the fear of death.
                                                  --Young.

            The brace of large greyhounds, who were the
            companions of his sports.             --Sir W.
                                                  Scott.

   2. One; any; one. [Obs., except in the archaic phrase, as who
      should say.]

            As who should say, it were a very dangerous matter
            if a man in any point should be found wiser than his
            forefathers were.                     --Robynson
                                                  (More's
                                                  Utopia).

Source : WordNet®

WHO
     n : a United Nations agency to coordinate international health
         activities and to help governments improve health
         services [syn: {World Health Organization}]