Done suddenly and roughly, with no politeness and no proper goodbye. The word points at a missing ceremony — no warning, no thanks, no soft words, no dignity for the person on the receiving end. Its home ground is endings and removals: an unceremonious exit, an unceremonious dismissal, an unceremonious end to a forty-year career. Someone was pushed out, and nobody bothered to make it graceful. Here is the important thing about this word in real English: the adverb unceremoniously is much, much more common than the adjective, and it lives in a small set of verbs — he was unceremoniously dumped, sacked, kicked out, bundled into a car, dropped on the pavement. If your students learn one form, learn that one. There is a lighter use too, without any cruelty in it: simply informal, without fuss. An unceremonious meal with old friends is a good thing — no speeches, no seating plan. Which meaning you get depends entirely on whether someone was hurt. Note also that it is not the opposite of ceremonious in a tidy way. Ceremonious means stiffly formal and slightly stuffy, and it is mildly negative itself; unceremonious is not its polite twin but its rude cousin.

草率無禮的、突然又不留情面的（常見於「被毫不客氣地趕走／開除」）。實際上副詞 unceremoniously 更常用。