To protect; defend; watch over; be on one's guard.
One who or that which protects or defends.
Watchful oversight; an attitude or condition of defence.
One having charge, as of a train, or of baggage.
I will keep guard till you are over." – Night and Morning, Volume 3 by Edward Bulwer Lytton
The guard stood aside. – Astounding Stories of Super-Science, March 1930 by Various