The Collaborative International Dictionary of English v.0.48:

Forefend \Fore*fend"\, v. t. [OE. forfenden; pref. for- + fenden
   to fend. See Fend, v. t.]
   To hinder; to fend off; to avert; to prevent the approach of;
   to forbid or prohibit. See Forfend.
   [1913 Webster]

         God forefend it should ever be recorded in our history.
                                                  --Landor.
   [1913 Webster]

         It would be a far better work . . . to forefend the
         cruelty.                                 --I. Taylor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

forefend
    v 1: prevent the occurrence of; prevent from happening; "Let's
         avoid a confrontation"; "head off a confrontation"; "avert
         a strike" [syn: debar, forefend, forfend, obviate,
         deflect, avert, head off, stave off, fend off,
         avoid, ward off]