The Collaborative International Dictionary of English v.0.48:

guy \guy\, n.
   1. A grotesque effigy, like that of Guy Fawkes, dressed up in
      England on the fifth of November, the day of the Gunpowder
      Plot.
      [1913 Webster]

            The lady . . . who dresses like a guy. --W. S.
                                                  Gilbert.
      [1913 Webster]

   2. Hence: A person of queer looks or dress. [Chiefly Brit.
      slang] --Dickens.
      [1913 Webster]

   3. A man or young man; a fellow; -- usually contrasted with
      gals or girls as, it was fun for both the guys and
      gals; the guys were watching football while the girls
      played bridge. [Informal]
      [PJC]

   4. A member of a group of either sex, usually a friend or
      comrade; -- usually used in the pl.; as, tell the guys to
      come inside; are any of you guys interested in a game of
      tennis?. [Informal]
      [PJC]

   great guy a man who has a very pleasant personality,
      typically one who is friendly, generous, and pleasant to
      associate with.
      [PJC]