The Collaborative International Dictionary of English v.0.48:

Rounder \Round"er\, n.
   1. One who rounds; one who comes about frequently or
      regularly.
      [1913 Webster]

   2. A tool for making an edge or surface round.
      [1913 Webster]

   3. pl. An English game somewhat resembling baseball; also,
      another English game resembling the game of fives, but
      played with a football.
      [1913 Webster]

            Now we play rounders, and then we played prisoner's
            base.                                 --Bagehot.
      [1913 Webster]

WordNet (r) 3.0 (2006):

rounder
    n 1: a dissolute person; usually a man who is morally
         unrestrained [syn: libertine, debauchee, rounder]
    2: a tool for rounding corners or edges