To Regret, To Mourn, To Lament
transitive verb, godan verb
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means regret and the verb vocab version is to regret or to mourn.
くやむ
The reading comes from 悔しい.
ガンガン響く頭と共に目を覚ます度に、前日の夜飲み過ぎたことを悔やみます。
Whenever I wake up with a pounding headache, I lament drinking too much the night before.