鋭 - SHARP Metal Tears Your Skin

Readings & Meanings:

エイ

するど（い）

sharp

Common Usage:

鋭い

鋭利

Examples:

怪しい男に鋭いナイフで刺された。

彼は鋭い観察眼を持っている。

鋭利な刃物で手を切ってしまった。

Translations:

I was stabbed with a knife by a suspicious-looking guy.

He has keen eyes.

I cut my hand with the sharp cutlery.

Radical:

Kane-hen on the left: 金

金 means metal or money. The idea is that the marks on either side of the 土 (earth) mark the spot where gold can be dug up.

兌 on the right, as a phonetic. It typically means "exchange," but if you look at its parts, it's got "divide left and right" on top (八). Think "tear, strip away."

So, with 鋭, picture metal sharp enough to tear your enemies to shreds.

Bonus:

You can use "鋭い" without any other words. If someone points out something very insightful, you can just say "するどい", and you will have given a really good compliment. Just like in English with "sharp!"

References:

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