perish the thought

from The Collaborative International Dictionary of English v.0.48

Perish \Per"ish\, v. t.
   To cause perish. [Obs.] --Bacon.
   [1913 Webster]

   {perish the thought} I hope it will never happen; -- a phrase
      used after mention of a possible undesirable event,
      sometimes facetiously.
      [PJC]