The terrible living conditions of migrant workers, he said, were an outrage.

outrage 是由前缀 out-（表示"超出"）和名词 rage（愤怒）组成的复合名词，字面意思是"超出正常范围的愤怒"，引申为"令人愤慨的行为或事件"。在这里指移民工人恶劣的生活条件这种令人极度愤怒的状况。