The English word militant is both an adjective and a noun, and it is generally used to mean vigorously active, combative and/or aggressive, especially in support of a cause, as in "militant reformers". It comes from the 15th century Latin "militare" meaning "to serve as a soldier". The related modern concept of the militia as a defensive organization against invaders grew out of the Anglo-Saxon fyrd. In times of crisis, the militiaman left his civilian duties and became a soldier until the emergency was over, when he returned to his civilian occupation.