A person who for reasons of conscience refuses to take part in warfare.
Webster's New World
One who on the basis of religious or moral principles refuses to bear arms or participate in military service.
A person who, due to religious belief, refuses to participate as a combatant in any war. By law, such an individual is exempt from serving as a combatant, but may be required to perform an alternative form of service to the country in a civilian or non-combatant military role.