Noun

1. A person who keeps watch over something or someone
2. The person who plays that position on a football team
3. A device designed to prevent injury or accidents
4. A posture of defence in boxing or fencing
5. The person who plays the position of guard on a basketball team
6. A military unit serving to protect some place or person
7. A precautionary measure warding off impending danger or damage or injury etc.
8. The duty of serving as a sentry
9. (american football) a position on the line of scrimmage
10. A position on a basketball team

Verb

1. To keep watch over
2. Watch over or shield from danger or harm; protect
3. Protect against a challenge or attack
4. Take precautions in order to avoid some unwanted consequence