Sink is an English verb which means to go down, to lower or to submerge. It is often used in the context of a ship sinking, an object being submerged in water or a person feeling overwhelmed by something. It can also be used figuratively when describing someone's feelings becoming heavier or more difficult to manage. For example, you might say "My spirits sank when I heard the news" or "His confidence sunk after failing the test".