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

Moby Thesaurus II by Grady Ward, 1.0:

76 Moby Thesaurus words for "rounder":
   Arab, Casanova, Don Juan, Lothario, bad lot, beach bum,
   beachcomber, beggar, bo, bum, bummer, debauchee, dissipater, dogie,
   free liver, gallant, gamin, gamine, gay deceiver, gay dog,
   good-for-nothing, guttersnipe, high liver, hobo, homeless waif,
   idler, lady-killer, landloper, lazzarone, libertine, loafer, losel,
   lover-boy, mudlark, night owl, nighthawk, no-good, philanderer,
   piker, profligate, ragamuffin, ragman, ragpicker, rake, rakehell,
   rip, roue, scapegrace, ski bum, skirt chaser, stiff, stray,
   street Arab, street urchin, sundowner, surf bum, swagman, swagsman,
   swinger, tatterdemalion, tennis bum, tramp, turnpiker, urchin, vag,
   vagabond, vagrant, waif, waifs and strays, walking phallus, wanton,
   waster, wastrel, wolf, woman chaser, womanizer