九(jiǔ) - nine in Mandarin

九 (jiǔ) is nine, the last of the single digits and the one with the best press after 八 (bā). It is a perfect homophone of 久 (jiǔ, long-lasting), so nine stands for longevity and for things that endure: nine roses for a sweetheart, a nine in a wedding date, and the Double Ninth festival on the ninth day of the ninth lunar month, when families honour the old. It also sounds exactly like 酒 (jiǔ, alcohol), which produces a steady supply of drinking puns and no deeper meaning.

It works like any other numeral: 九个人 (jiǔ ge rén, nine people), 九点 (jiǔ diǎn, nine o'clock), 九块钱 (jiǔ kuài qián, nine yuan). 九月 (jiǔyuè) is September, 九号 (jiǔ hào) is the ninth of the month, and ninth in a sequence is 第九 (dì jiǔ). Above ten it slots in the same way: 十九 (shíjiǔ) is nineteen and 九十 (jiǔshí) is ninety.

Being a third tone, 九 follows the ordinary third-tone rule. Before another third tone it rises, so 九点 sounds like jiú diǎn; before anything else it dips low and stays there. That is not special to 九, it is just the tone system doing its job, and unlike the optional lift on 七 (qī) and 八 (bā) it is a change you must actually make.