principal / principle

principal: adjective meaning 'the most important'

principal：形容词，意思是“最重要的”

Examples:

例句：

The principal reason for my decision was the money.

What are the principal irregular verbs?

我做决定时最看重的就是钱。

最重要的不规则动词有哪些？

principle: a rule (usually in science but also concerning morals)

principle：定律、原则（通常用在科学领域，不过也用在相关的道德领域）

Examples:

例句：

It's the first principle of aerodynamics.

He has very loose principles.

这是热力学定律。

他的原则弹性很大。