The Collaborative International Dictionary of English v.0.48:

Lobby \Lob"by\, n.; pl. Lobbies. [LL. lobium, lobia, laubia, a
   covered portico fit for walking, fr. OHG. louba, G. laube,
   arbor. See Lodge.]
   1. (Arch.) A passage or hall of communication, especially
      when large enough to serve also as a waiting room. It
      differs from an antechamber in that a lobby communicates
      between several rooms, an antechamber to one only; but
      this distinction is not carefully preserved.
      [1913 Webster]

   2. That part of a hall of legislation not appropriated to the
      official use of the assembly; hence, the persons,
      collectively, who frequent such a place to transact
      business with the legislators; hence: any persons, not
      members of a legislative body, who strive to influence its
      proceedings by personal agency; a group of lobbyists for a
      particular cause; as, the drug industry lobby. [U. S.]
      [1913 Webster +PJC]

   3. (Naut.) An apartment or passageway in the fore part of an
      old-fashioned cabin under the quarter-deck.
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   4. (Agric.) A confined place for cattle, formed by hedges.
      trees, or other fencing, near the farmyard.
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   Lobby member, a lobbyist. [Humorous cant, U. S.]
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