[1] : 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
see also:
perish the thought 

Thought >> T Words
Thought, definition of term: Thought
thought_pag1.html

Perish >> P Words
Perish, definition of term: Perish
perish_pag1.html