knight of the post

idiomatic obsolete

(obsolete, idiomatic) A known perjurer; a professional false witness.

Japanese Meaning

（古語・慣用表現）偽証者、すなわち嘘の証言をすることで知られている人物。 / （転じて）虚偽の証言を行う人、偽証の専門家

Everybody in the courtroom knew he was a knight of the post, so his testimony carried no weight.

法廷にいた誰もが彼が悪名高い偽証者だと知っていたので、彼の証言は重く受け止められなかった。

Sense（1）

(obsolete, idiomatic) A known perjurer; a professional false witness.

[…] But with more lucky hit than those

That use to make the stars depose,

Like knights o' th' post, and falsely charge

Upon themselves what others forge;

As if they were consenting to

All mischief in the world men do […]

knights of the post

（ plural ）