flaw

你的推理中有一个缺陷。

There's a ___flaw in your reasoning.

这颗钻石唯一的瑕疵是一个小划痕。

The diamond's only ___flaw is a tiny scratch.

这个论点起初看似有说服力，但包含一个根本性的缺陷。

The argument seems convincing at first, but it contains a fundamental ___flaw.