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 21, 2005
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 9, 2006
on9 (憨鳩) is a Cantonese swear word which means foolish, stupid and brainless.
It is pronounced as 'on' + 'gau'. ('gau' is the Cantonese pronunciation of '9')
It is a friendly swear word to laugh, scold or discriminate other ppl.

on99 (憨鳩鳩): very foolish
on9 zai (憨鳩仔): a foolish guy
on lun 7 9 (憨撚柒鳩): extremely stupid, mostly used to scold others when angry
on gui (憨居): a less violent way to say on9
Person 1: The guy steps on a piece of shit and slips.
Person 2: HAHA, he is really on9.
by ccthz November 22, 2021
It is short term of online

Feels very happy, short term as on cloud nine Or
Word for appreciation, which is upper than 1-9, and greater than them, for appreciating people who done very good advancement
When he on9s, he feel on9, and do a very on9 thing
by PolyMoster April 22, 2022
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 8, 2021