Wiktionary
perish the thought
phr. May the thought perish; said of an idea or suggestion which is undesirable.
Usage examples of "perish the thought".
The rest was his own fear that these ridiculous and vastly mad people could somehow slaughter his bright, brave Maggie as she risked herself in her own bullheaded way to save them, as he had no doubt she was already doing unless, perish the thought, she was instead providing nourishment for the loathsome wolf-man.
Until such time, he would simply have to accept whatever posting Borga assigned him, though it chilled him even to imagine being sent to somewhere like Sriluur, Kessel, or-perish the thought-Tatooine.
With these Americans, I can't predict how soon I'll require your talents again, anyway, perish the thought.