Definitions
American Heritage® Dictionary of the English Language, Fourth Edition
- n. Informal Something unacceptable or impermissible: "Even though his company wasn't the one involved in the case, what he did is considered a definite no-no” ( Mike Royko).
- n. Informal A social blunder; a faux pas.
Wiktionary
- n. Something that is forbidden, prohibited, discouraged or taboo.
- n. A no-hitter; a game in which no batter on one of the teams got a hit.
- n. A no hitter, a game in which no batter on one of the teams has gotten a hit yet.
GNU Webster's 1913
- n. Something improper, unethical, inadvisable, or illegal.
Examples
“Even information about the swimsuit is a no-no in Saudi Arabia, where a vigilant government blocks Western websites displaying or advertising the sale of bikinis.”
“Had he been able to finish off another no-no, Verlander would have become just the sixth player in baseball history to throw three or more no-hitters, and yet he still would have only been 43% of the way to matching Ryan's mark.”
The Wall Street Journal: A Record More Daunting Than DiMaggio's 56
“If we just had a private plane for our personal pleasure, that would be a big no-no.”
The Wall Street Journal: Corporate Jet Set: Leisure vs. Business
“And forget drinking, that's a no-no, something about the ingredients in booze that could compromise my already weakened immune system.”
“Some brands are taking great pains to ease men into the idea of tucking a short-sleeve woven shirt in pants, previously a fashion no-no.”
The Wall Street Journal: Stylish Guys Steal Short Sleeves From Nerds
“Do you have a suggestion for our list of Twitter no-no's?”
The Huffington Post: What Not To Post On Twitter: 11 Things Your Tweeps Don't Need To Know
“Burmudas, black knee socks and wing-tips are my only no-no”
“I and my tourist companions in a van were nearly lynched in Nairobi in 1969 when some idiot tourist took a photograph of people in a busy market in that city one day; a no-no in any sensible person´s book.”
“While I understand the rationale, and I think a lot of folks can accept the same when told, in the absence of any explanation, people tend to believe that the thread was locked because the topic is a no-no.”
“Others have mentioned it and I agree, that when a thread is locked, I wonder who did a no-no, other than wandering off into the yonder.”
Lists
These user-created lists contain the word ‘no-no’.
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Hyphenated Repeats
Exactly reduplicated words connected by a hyphen.
aye-aye, cleek-cleek, arc-arc, killy-killy, dum-dum, tom-tom, argon-argon, carbon-carbon, win-win, lose-lose, bye-bye, choo-choo and 101 more...

bilby No-no is not a double negative in the conventional sense. Ain't you never seen one o' those? May 30, 2011
jmjarmstrong JM thinks double negatives are a no-no. May 30, 2011