害 - Cover Your Mouth before You HARM Someone

Readings & Meanings:

カイ

harm, calamity

Common Usage:

百害あって一利なし

公害

Examples:

テレビは子供にとって百害あって一利なし、だ。

中国の公害問題が心配だ。

Translations:

For children, TV has a hundred harmful points and not one single benefit.

I'm worried about the Chinese pollution issue.

Radical:

宀 is the radical... have I dealt with this before? I guess not directly.

This is the う-crown, U-kammuri. It's called that because it looks like the top of the katakana ウ. It is a pictograph of a roof or some kind of cover.

口, mouth, is also in there. Everything above the mouth element indicates something covering the mouth. It looks painful.

If your speech is hindered, you are probably damaged or harmed.

References:

http://www.kanjinetworks.com/indices/radindex.html
http://www.thejapanesepage.com/node/kanji/ka.htm