Vulgar
Used in Hong Kong
Pronunciation: "on-gau" ("on" in English, "9" in Cantonese)
Meaning: stupid, thinking stupid
More: on99
Chief Exceutive Mr.Tung: If China is good, Hong Kong will be good. When Hong Kong is good, we are good too.
Citizen A: He's on9.
Citizen B: He's on99.
by HKboy February 20, 2005
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adj. Very stupid or foolish.
Pronounced "on gau" (The 9 is pronounced in Cantonese)

Cantonese slang used mainly by young Hong Kong Chinese. First originated on the Internet (isn't everything) but soon spread to everyday speech.

Originates from two words:
The first part "on" comes from "On ghuy" - a cantonese slang word meaning foolish.
The second part "9" comes from "gau" - a cantonese slang word meaning penis.

Also used as part of the phrase "on9 zai" meaning foolish man/boy.
Dude 1: Wow, that silly mainlander squatting on the pavement looks so damn on9.

Dude 2: Shut up, you on9 zai.
by The loch monster August 08, 2006
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This word is commonly used in Hong Kong.
It means the person is very stupid, doing childish and stupid things, or saying something that is nonsense.
by The invisible guy December 31, 2019
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Mostly used in Hong Kong
Cantonese slang word
Spelling in english: On gau/gao
9 is pronounced "gau" in Cantonese
Which also means penis or dick
It means foolish, stupid, dumb, especially when describing someone's actions or speech even appearance but not specifically about the target's intelligence.
This word is commonly used among youngsters, as it is mildly offensive yet usually in a funny way. Still it can be aggressive and provoking sometimes if the tone is not friendly or used in a swearing sentence.
In numerous cases, it is transformed into on99 or on-lun-9. The meanings are basically the same.
Hong Kong:
Cayden just said a lame joke to flirt girls, he didn't realize it was really cringy and on9.
Look! Ken just did his hair bald and it definitely doesn't suit him, it looks so on9 lol.
Matthew is very on9, he always slap his classmates' asses just to irritate them for no good reason at all! Then he escapes and laughs in a cheeky way, I genuinely don't understand his kind of humour.
US:
Memes are so on9 yet entertaining at the same time!
Filthy Frank is the most on9 youtuber I've ever seen.
UK:
Undoubtly, Mr. Bean is the on9 representative of cartoons.
by BeforeChrist March 12, 2019
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A slang from Hong Kong which means extremely stupid and dumb
e.g. Ricegum is so on9 that everybody make fun of him
by Nejshhd July 07, 2021
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