The definition of a no no is something that should not be done or something that is against the rules.(noun)
An example of a no no is eating cookies before dinner after your mom said not to eat them.
See no-no in Webster's New World College Dictionary
noun pl. no-nos
Origin: < No! No!, as said in admonishing a young child
See no-no in American Heritage Dictionary 4
noun pl. no-noes
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