Fist
noun
The kanji and the word are exactly the same. That means they share meanings as well.
こぶし
Since this word is made up of a single kanji, it probably uses the kun'yomi reading. You did not learn this reading, so here's a mnemonic to help you to remember: You make a fist. Why? Because she stole your corn on the cob. "Cob! She (こぶし) stole my cob!"
彼は拳についた血をハンカチで拭いました。
He cleaned the blood off his fist with his handkerchief.