noun
bad guy; scoundrel; wicked person
Refers to a person who is morally bad or a troublemaker. Often used in casual or slangy speech.
あいつは本当に悪だな。
That guy is a real scoundrel.
彼は見かけによらず悪だ。
He's a bad guy despite his appearance.
noun
bad child; brat; naughty kid
Used for a misbehaving child. Often affectionate or scolding depending on tone.
うちの子は本当に悪で、言うことを聞かない。
My kid is a real brat and never listens.
noun, used as a prefix
bad thing; mischief
Used as a prefix in compounds like 悪さ (mischief) or 悪知恵 (cunning). Not a standalone noun for 'bad thing'.
悪さをする子は嫌われる。
Kids who do mischief are disliked.
彼は悪知恵が働く。
He's cunning (lit. has bad wisdom).
noun-modifying (irregular)
excessive; unrestrained; overindulgent
Prenominal use, often in set phrases like 悪酔い (getting sick from drinking too much) or 悪ふざけ (excessive prank). Not freely productive.
悪ふざけが過ぎて先生に怒られた。
He got scolded by the teacher for excessive pranks.
悪酔いしないように気をつけて。
Be careful not to drink too much and get sick.
From Old Japanese. The kanji 悪 is used for its meaning 'bad, evil'. The reading わる is a native Japanese word, not a Sino-Japanese borrowing.