The Collaborative International Dictionary of English v.0.48:

Chairman \Chair"man\, n.; pl. Chairmen.
   1. The presiding officer of a committee, or of a public or
      private meeting, or of any organized body.
      [1913 Webster]

   2. One whose business it is to cary a chair or sedan.
      [1913 Webster]

            Breaks watchmen's heads and chairmen's glasses.
                                                  --Prior.
      [1913 Webster]

WordNet (r) 3.0 (2006):

chairman
    n 1: the officer who presides at the meetings of an
         organization; "address your remarks to the chairperson"
         [syn: president, chairman, chairwoman, chair,
         chairperson]
    v 1: act or preside as chair, as of an academic department in a
         university; "She chaired the department for many years"
         [syn: chair, chairman]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

CHAIRMAN. The presiding officer of a committee; as, chairman of the
committee of ways and means. The person selected to preside over a popular
meeting, is also  called a chairman or moderator.