society > armed hostility > armed forces > the Army > group with special function or duty > [noun] > for guard duty > subsidiary (3)
An extra guard to check another guard, or to be a reserve defence. Obsolete.
A small guard, originally mounted a short distance in front of each battalion in a camp, and now having mainly ceremonial duties.
A ward or guard which is not the main one; as in the Byward Tower in the Tower of London.