lifeguard

Short definition from Wiktionary

Noun

1. 1
   A lifesaver: a rescuer, usually an expert swimmer, employed to save swimmers in trouble or near drowning at a body of water.
2. 2
   A bodyguard or unit of bodyguards, a guard of someone's (especially a king's) life or person.
3. 3
   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.