flaw
"Flaw" is a very useful word in everyday English with a couple of closely related meanings. It refers to something that is wrong, imperfect, or weak — whether in an object, a plan, or even a person's character.
A flaw is a small fault or defect in something physical — a crack, a scratch, or any part that is not quite right. Think of a beautiful vase with a tiny crack in it. That crack is a flaw. It does not have to ruin the whole thing, but it stops it from being perfect.
everyday language · Modern, widely used
A flaw can also be a mistake or weak point in a plan, idea, or argument — something that makes it less reliable or likely to fail. Imagine you have a great business plan, but you forgot to think about the costs. That missing piece is a flaw in your plan.
everyday language, academic, business · Modern, widely used · figurative
When talking about people, a flaw is a negative quality or weakness in someone's personality. Nobody is perfect, so everyone has flaws. A person might be kind but impatient — that impatience is a character flaw. This use is not always harsh; it is simply honest.
everyday language, literature · Modern, widely used · figurative
As a verb, 'to flaw' means to introduce a fault or weakness into something. This form is less common — you will mostly see it in the past participle 'flawed', which means something already has a flaw in it.
formal writing, everyday language · Modern, though 'flawed' is far more common than the verb form