If a person is embittered, they have become angry, sad, or full of hate because of bad or unfair things that happened to them. This is the form you will meet most often — a word for a person (or sometimes a voice, a look, a comment) that has gone sour and stayed that way. An embittered worker may still do the job, but the warmth is gone. Though actually it does not only mean “a bit annoyed.” It points to a deep, lasting change: the unfairness has got into them. Younger speakers may just say “bitter” or “still angry about it”; embittered sounds a little more formal, like a newspaper or a novel.