militant

The word militant, which is both an adjective and a noun, usually is used to mean vigorously active, combative and 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 and life.