警告某人的英文：
warn of

Make a bell sound to call,warn,etc sb
鸣铃召唤、警告...某人

Warn sb that his behaviour is unacceptableand will no longer be tolerated
警告某人其行为已令人无法忍受.

Give sb private information;warn sb secretly
向某人透露秘密消息;暗中警告某人.

They warned him to be careful.
他们告诫过他要小心。

Seismal Microcosmic Warning Signs
地震微观前兆

She yelled a warning to us.
她大声警告我们。

They attacked without a warning.
他们不宣而战。

The police are warning of possible delays.
警方通知交通可能受阻。