Hello Monmon,

This is an very interesting question. How does one now that in pí jiǔ, jiǔ 酒 means ‘alcohol’ and not jiu “9” 九 or 就 “jiu” come near or jiu 旧 “old”, or jiu 久 “long time” or jiu 舅 “mothers brother”.
Well first of all there are 4 tones, thus the meaning depends on the tone, like jiu 旧 “old”, is in the 4th tone, whilst jiǔ 酒 is spoken in the third tone.
But there are much more characters then four pronounced jiu, meaning that a lot of them can have the same sound and tone, so how can you tell then. Well context, that is if you hear pijiu [bear] you know jiu hear means alcohol, if you hear shijiu 19, jiu here must mean nine.
When Chinese are not clear about the meaning of a character they might ask, you mean pijiu de jiu 你的意思是啤酒的酒？to be sure that both visualize the same character and talk about the same thing.
Modern Chinese is for the most part disyllabic, that is two characters (syllables) for one word (meaning), old Chinese was monosyllabic one character for one word, when spoken it was almost impossible to understand what is meant, since each character could have so many meanings with very view clues as to the meaning meant. Only when reading the old Chinese text the meaning becomes clear.
Chinese is full with word jokes because of this“毛主席万岁，
Mao zu xi (Maozhidong) Wan sui, meaning Maozhidong ten thousand years! would be written as 毛主席万税
Maozhidong ten thousand tax, 岁 sui meaning years, and 税 shui meaning tax.
So in short when ever you go to China be careful what and how you speak, before you know it you will call 骂ma4=scold your mother 妈 ma1, a horse 马 ma3, better call her ma3 玛=jade!

success

[如果我冒犯别人，情抱歉我，我还是中国学生]

万事如意

路蓝克