Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means sink so the verb vocab version is to sink.

This is a transitive verb, so it's used when you're sinking something else. You can differentiate it from the intransitive 沈む by imaging that you're watching an enemy ship sink, and they shout out, "Who did this to me!" You respond, me (め). I did."