To Worry
To Be Troubled
godan verb
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means worry so the verb vocab version is to worry.
The reading is the same as what you learned with the kanji, so no need to worry about it.
「どうしたの？何を悩んでいるの？」「昨日、彼女に振られたんだ。」
"Hey! What’s troubling you?" "My girlfriend dumped me last night."