"Chink" is a type of weakness. It is usually a crack, or sometimes a bundling-up in a rope or a chain. It’s used too often in American English, perhaps in part because it’s also a pejorative slang term for Chinese people.

It is true that we don't use it anymore as it is a racial slur mostly against Chinese people but also many other asians. You will find it in old book and texts however.

A chink is a narrow space, gap or crack. By itself, it doesn't automatically indicate a weakness, but a gap or crack where there shouldn't be does indicate a fault. "A chink in one's armour" means a weak spot; an Achilles' heel.

Weakness is just a normal, everyday word. That other word (I don't even dare type it) is very very very very very VERY offensive and should never be used by anyone to describe an Asian person.