If a person is unapproachable, they give off a feeling that says "don't come and talk to me" — so people don't. Note carefully what this word does and does not claim. It is not about whether the person is actually unkind. It is about the impression they make: a face that never softens, a voice that stays flat, an office door that is always shut. Plenty of unapproachable people are perfectly nice once you get past the first minute — which is exactly why students and workers say it with a little frustration. "She seems unapproachable" often means "I need help but I can't make myself go and ask." That is the real weight of the word: it names a barrier that stops a conversation before it starts. It is used mostly about people in some position above you — a boss, a teacher, a senior colleague, a famous person — because with an equal you would just say "unfriendly" or "cold". You will very often see it with "seem", "appear", or "come across as", precisely because speakers know they are reporting a feeling, not a fact. The opposite, approachable, is high praise in a job reference here. There is a second, much rarer use for places rather than people — a cliff or an island that is unapproachable is one you physically cannot get near — but in everyday speech it is nearly always about a person.