To unnerve someone is to shake them inside, so that the steadiness they normally have goes away. It is not the same as scaring someone. If a car nearly hits you, you are scared — your body jumps, and a minute later you are fine. If something unnerves you, the effect is quieter and it stays: you feel a little wrong, a little off, and you cannot think as clearly or act as confidently as you usually do. A student who is unnerved by a hard first question may then do badly on the easy questions after it — that is the real damage. The things that unnerve people are often small and strange rather than big and loud: someone smiling at you when they should be angry, a phone call at 3 a.m., a room that is too quiet, being watched while you work. It is usually used in the passive — 'I was unnerved by…' — because it is about what happened to you, not about someone choosing to do it. Someone CAN do it on purpose, though: a chess player or a lawyer may try to unnerve an opponent by staying calm and saying nothing. It is a slightly literary word; in speech people more often say 'it freaked me out' or 'it gave me a bad feeling', and they save 'unnerve' for writing or for careful speech.

使人心神不寧、亂了方寸。不是「嚇一跳」（那是 startle／嚇到），比較接近「毛毛的、心裡發慌，整個人定不下來」。中文可以說「令人不安」，但要注意：unnerve 強調的是「原本的鎮定被抽掉了」，所以「亂了陣腳」有時更貼切。