To Sink Something
transitive verb, ichidan verb
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."
When you sink something, like a battleship, you go on and say: "she's (しず) sunk, I sunk her." That's like your tagline, or something. You say it for some reason because you think it's cool.
彼はソファに身を沈めながら、アカデミー賞の授賞式の生中継を観ています。
He is watching the broadcast of the Academy Awards ceremony and sinking into the sofa.