noun, plural no-nos, no-no's. Informal.

anything that is forbidden or not advisable, as because of being improper or unsafe: If you want to lose weight, rich desserts are a no-no.

Origin of no-no

1940–45, Americanism; reduplication of no1 Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Word Origin and History for no-nos



1942, from reduplication of no.

Online Etymology Dictionary, © 2010 Douglas Harper