The Collaborative International Dictionary of English v.0.48:

Relieving \Re*liev"ing\, a.
   Serving or tending to relieve.
   [1913 Webster]

   Relieving arch (Arch.), a discharging arch. See under
      Discharge, v. t.

   Relieving tackle. (Naut.)
   (a) A temporary tackle attached to the tiller of a vessel
       during gales or an action, in case of accident to the
       tiller ropes.
   (b) A strong tackle from a wharf to a careened vessel, to
       prevent her from going over entirely, and to assist in
       righting her. --Totten. --Craig.
       [1913 Webster]