A member of a troop of citizens raised to reinforce the regular army. In later use: specifically a member of the Milice, the force employed by the Vichy government of 1940–4 to repress internal dissent.
Origin
Mid 18th century. From French milicien a member of a troop of citizens raised to reinforce the regular army, a member of the Milice of Vichy from milice + -ien.