lifeguard

(uncommon) A bodyguard or unit of bodyguards, a guard of someone's (especially a king's) life or person.

An attendant, usually an expert swimmer, employed to save swimmers in trouble or near drowning at a body of water.

A lifesaver.

(rail transport) 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.