厉 (lì) is a bound form (b.f.) — it cannot stand alone as a full word in modern Chinese. You'll only see it as the first character in compound words like 厉害 (lìhai, 'impressive, severe') and 严厉 (yánlì, 'strict, severe'). Its core meaning is 'harsh, severe, strict', and it carries a negative or intense tone. As a surname, it's pronounced Lì and is relatively rare.