swear an oath

Barons had to swear an oath of allegiance to the king.

贵族须宣誓效忠国王。

To swear falsely; commit perjury. Before giving evidence you have to swear an oath.

作伪证发伪誓，作伪证在作证之前你得先发誓。

Before giving evidence you have to swear an oath.

在作证之前你得先发誓.

To state that you will tell the truth, but without swear an oath.

未经宣誓声明你要说真话。

to take/swear an oath of allegiance

宣誓效忠

In court you have to swear an oath that you will tell the truth.

在法庭上你必须发誓自己说的一切话都是真的.

However, he also instituted a hierarchical system of levels among his followers, and had them swear an oath on his core tenets.

不过，他也在追随者中间立了标准等级制度，它让追随者以他的核心信条宣誓。

For anyone to become a member of it, they must first swear an oath.

要想成为其中的一员, 首先要起誓.

Government employees swear an oath not to reveal official secrets.

政府雇员宣誓不泄露官方机密.