The Collaborative International Dictionary of English v.0.48:

Retiring \Re*tir"ing\, a.
   1. Reserved; shy; not forward or obtrusive; as, retiring
      modesty; retiring manners.
      [1913 Webster]

   2. Of or pertaining to retirement; causing retirement; suited
      to, or belonging to, retirement.
      [1913 Webster]

   Retiring board (Mil.), a board of officers who consider and
      report upon the alleged incapacity of an officer for
      active service.

   Retiring pension, a pension granted to a public officer on
      his retirement from office or service.
      [1913 Webster]