Thought but not spoken. `Unsaid` almost always turns up in one fixed shape: something is *left* unsaid. That little word 'left' does a lot of work — it means the thing was there, available, could have been said, and someone chose silence instead. So it is not the same as 'nothing was said'. It points at a specific unspoken thing hanging in the room.

The feeling around it is usually heavy. 'Some things are better left unsaid' is what people say about a truth that would only hurt. 'So much was left unsaid between them' is what you write about two people who parted badly. There is often regret, tact, or tension in it. Occasionally it is warm — an understanding so complete it needs no words — but the sad reading is far more common.

It is a past participle used as an adjective, and it sits after the verb (left unsaid, remained unsaid, went unsaid) far more often than before a noun. 'The unsaid words' is possible in writing but sounds arranged; 'unspoken' is the word most people reach for in front of a noun.