guard
noun
a person who keeps watch over something or someone
the person who plays that position on a football team
“the left guard was injured on the play”
a device designed to prevent injury or accidents
a posture of defence in boxing or fencing
“keep your guard up”
the person who plays the position of guard on a basketball team
a military unit serving to protect some place or person
a precautionary measure warding off impending danger or damage or injury etc.
“he put an ice pack on the injury as a precaution”
“an insurance policy is a good safeguard”
the duty of serving as a sentry
“he was on guard that night”
(American football) a position on the line of scrimmage
“guards must be good blockers”
a position on a basketball team
verb
to keep watch over
“there would be men guarding the horses”
watch over or shield from danger or harm; protect
“guard my possessions while I'm away”
Synonymswardprotect against a challenge or attack
“Hold that position behind the trees!”
“Hold the bridge against the enemy's attacks”
take precautions in order to avoid some unwanted consequence
“guard against becoming too friendly with the staff”
“guard against infection”
Source: WordNet 3.1, Princeton University