lifeguard

1. (uncommon) A bodyguard or unit of bodyguards, a guard of someone's (especially a king's) life or person.Examples: ""The people's love is the king's lifeguard.""; "[I]n the reserve were the king's lifeguard, commanded by the earl of Lindsey, and prince Rupert's regiment of foot[.]"; "Constantine the Great is known to have raised the five scholae of horsemen who formed the actual lifeguard of the prince, and followed his person whenever he went out to war."uncommon

2. (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.Examples: "It also looked at what effect stronger lifeguards might have had. They protect the leading wheels from small obstacles and in modern trains have coped with hitting landslip debris."