Yes, sank is a Scrabble word!

Verb

1. Fall or descend to a lower place or level

2. Cause to sink

3. Pass into a specified state or condition

4. Go under, "The raft sank and its occupants drowned"

5. Descend into or as if into some soft substance or place

6. Appear to move downward

7. Fall heavily or suddenly; decline markedly

8. Fall or sink heavily

9. Embed deeply