害(hài) - to harm, to cause trouble to, harm in Mandarin

害 (hài) means to harm. In modern Mandarin it mostly appears inside compounds, so the ones to learn first are 伤害 (to injure or hurt), 有害 (harmful), 害虫 (a pest) and 害怕 (to be afraid, where 害 is doing something closer to suffer).

Where the bare character earns its keep is the pattern 害得, which lays blame. 害得我迟到 means you made me late and it was your doing, with a note of complaint that plain 让 or 使 does not carry. English needs a whole clause for this: "because of you I was late". Mandarin gets there in one verb, and using it well is a genuine step up in naturalness.

The trap is 害怕. Learners meet it early and reasonably assume 害 must mean fear, then try 我很害 for I am scared. It is not a word on its own in that sense. Fear is 害怕 or 怕, and the bare 害 is only ever about the damage you do to someone else.