Describes a firm, unyielding attitude or a grave, dignified manner. Often used with verbs like 言う, 命じる, or 立つ.
He sternly refuses to tolerate dishonesty.
The president resolutely ordered reforms.
Rare alternative kanji form; 厳として is much more common.
From the kanji 厳 (strict, solemn) combined with the adverbial particle として, forming a set phrase meaning 'in a strict/solemn manner'.