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to get angry; to get mad
to be angular; to be square
「怒る」 has another reading with different meanings.
彼は不正に対して怒った。
He got angry at the injustice.
怒るべき時には怒るべきだ。
One should get angry when necessary.
天が怒るように雷が鳴った。
Thunder roared as if the heavens were angry.