The Collaborative International Dictionary of English v.0.48:

Guardian \Guard"i*an\, n. [OF. guardain, gardien, F. gardien,
   LL. guardianus. See Guard, v. t., and cf. Wasden.]
   1. One who guards, preserves, or secures; one to whom any
      person or thing is committed for protection, security, or
      preservation from injury; a warden.
      [1913 Webster]

   2. (Law) One who has, or is entitled to, the custody of the
      person or property of an infant, a minor without living
      parents, or a person incapable of managing his own
      affairs.
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            Of the several species of guardians, the first are
            guardians by nature. -- viz., the father and (in
            some cases) the mother of the child.  --Blackstone.
      [1913 Webster]

   Guardian ad litem(Law), a guardian appointed by a court of
      justice to conduct a particular suit.

   Guardians of the poor, the members of a board appointed or
      elected to care for the relief of the poor within a
      township, or district.
      [1913 Webster]