厉害 (lì hai) is a versatile adjective meaning 'impressive,' 'formidable,' or 'awesome'—often expressing admiration, awe, or even mild alarm at someone’s skill, intensity, or unexpected ability. Though the characters 厉 (strict, severe) and 害 (harm, damage) literally suggest something threatening, in modern colloquial usage the word has softened significantly and is overwhelmingly positive or neutral. It frequently appears after verbs like 'is' (是), 'looks' (看起来), or 'seems' (显得), and can modify people, actions, objects, or situations.

The word is especially common in informal speech among young people and carries emotional weight—it conveys genuine reaction, not just description. You might call a basketball player’s dunk 厉害, praise a friend’s cooking as 厉害, or even exclaim 厉害！ when surprised by good news. Its tone is conversational and emphatic; formal writing tends to use more precise alternatives like 卓越 (zhuóyuè, 'outstanding') or 强大 (qiángdà, 'powerful').