n.

1. a person who keeps watch over something or someone
2. the person who plays that position on a football team
   
   • the left guard was injured on the play
3. a device designed to prevent injury;
   safety, safety device
4. a posture of defence in boxing or fencing
   
   • keep your guard up
5. the person who plays the position of guard on a basketball team
6. a group of men who escort and protect some important person;
   bodyguard
7. a precautionary measure warding off impending danger or damage or injury etc.;
   precaution, safeguard
   
   • he put an ice pack on the injury as a precaution
   • an insurance policy is a good safeguard
   • we let our guard down
8. the duty of serving as a sentry;
   guard duty, sentry duty, sentry go
   
   • he was on guard that night
9. a position on the line of scrimmage
   
   • guards must be good blockers
10. a position on a basketball team

v.

1. to keep watch over
   
   • there would be men guarding the horses
2. watch over or shield from danger or harm; protect;
   ward
   
   • guard my possessions while I'm away
3. protect against a challenge or attack;
   defend, hold
   
   • Hold that position behind the trees!
   • Hold the bridge against the enemy's attacks
4. take precautions in order to avoid some unwanted consequence
   
   • guard against becoming too friendly with the staff
   • guard against infection