Definition of "no-no" in English

noun

1. (colloquial, often childish) Something that is forbidden, prohibited, discouraged or taboo.

   • Smoking indoors is becoming a real no-no these days, in many places.

2. (baseball, colloquial) A no-hitter; a game in which no batter on one of the teams got a hit.

   • He threw two no-nos in his career.