Guard

A person who, or thing that, protects or watches over something.

"The prison guard unlocked the door of the cell.   After completing the repairs, he replaced the sump guard."

A garda; a police officer.

A squad responsible for protecting something.

"The president inspected the guard of honour."

The part of a sword that protects the wielder's hand.

To protect from danger; to secure against surprise, attack, or injury; to keep in safety; to defend.

To keep watch over, in order to prevent escape or restrain from acts of violence, or the like.

"Guard the prisoner."

To watch by way of caution or defense; to be caution; to be in a state or position of defense or safety.

"Careful people guard against mistakes."

To protect the edge of, especially with an ornamental border; hence, to face or ornament with lists, laces, etc.