Bitterness is a sharp, unpleasant feeling that develops when disappointment or hurt feelings linger and harden over time. When someone experiences bitterness, they hold onto anger or resentment long after the original problem occurred, like a wound that never quite heals.

You might see bitterness when a student who didn't make the team continues to complain about it months later, or when someone brings up an old argument every time they're upset about something new. While feeling hurt or disappointed is natural and normal, bitterness happens when those feelings get stuck and start coloring how you see everything else.

The word connects to the bitter taste of certain foods, like unsweetened cocoa or citrus peel: it's sharp, unpleasant, and hard to ignore. When people describe someone as bitter, they mean that person has let old hurts sour their outlook. A bitter comment is tinged with old resentment.