Sank is the past tense of the verb sink, which means to go down below the surface of water or another liquid. When a heavy rock sinks to the bottom of a pond, or when a ship takes on water and disappears beneath the waves, we say it sank.

The word often carries a sense of something going down that you didn't want to go down. The Titanic sank in 1912 after hitting an iceberg. A toy boat might sink in the bathtub if it gets a hole in it. Things sink because they're too heavy for the water to hold up: a stone sinks while a wooden stick floats.

You can also use sank to describe feelings dropping suddenly. Your heart might sink when you realize you forgot your homework at home, meaning you suddenly feel disappointed or worried. Or someone's spirits might sink after hearing bad news. When you say your stomach sank, you're describing that dropping feeling of dread or nervousness.

The word sank tells us that whatever went down has already gone down: it's finished. If something is going down right now, we say it sinks or is sinking. If it went down yesterday, it sank.