perish the thought - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Don't even think of it. This expression is used as a wish that what was just mentioned will never happen. For example, He's going to give another speech? Perish the thought! This phrase appeared in Handel's oratorio Joshua (1748; text by Thomas Morell): “It never shall be said that our allies in vain implor'd our aid. Perish the thought!” Also see god forbid.