The Collaborative International Dictionary of English v.0.48:

Swinger \Swing"er\, n.
   One who swings or whirls.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Swinger \Swin"ger\, n.
   1. One who swinges.
      [1913 Webster]

   2. Anything very large, forcible, or astonishing. [Obs. or
      Colloq.] --Herrick.
      [1913 Webster]

WordNet (r) 3.0 (2006):

swinger
    n 1: someone who swings sports implements
    2: a person who engages freely in promiscuous sex [syn:
       swinger, tramp]