鋭 sharp

Fonzie says "EYYYY!!" as he sticks his sharp thumb up, to indicate his satisfaction.

Older brother has a sharp mind so he winds up earning a lot of gold.

quick-witted, keen. ★☆☆☆☆
鋭 (sharp) + 敏 (agile / sensitive) = 鋭敏 (quick-witted, keen.)