Lifeguard

noun

1. A bodyguard or unit of bodyguards, a guard of someone's (especially a king's) life or person.
2. An attendant, usually an expert swimmer, employed to save swimmers in trouble or near drowning at a body of water.
3. A lifesaver.
4. A sturdy metal bracket fixed in front of each of the leading wheels of a train to deflect small objects away from the wheels to prevent derailment.