The young teacher firmly asserted her authority on the first day by setting clear rules.

asserted 是动词 assert 的过去式，assert 由前缀 as-（表示"加强"）和词根 sert（来自拉丁语，意为"加入、连接"）组成，字面意思是"强烈地加入/表明"，引申为"坚定地宣称、维护（权威等）"。