lifeguard

• life-guard (dated)

life +‎ guard, Calque of Dutch lijfgarde, where life has the sense of Dutch lijf (“body”) hence bodyguard[1]. Compare German Leibgarde (“bodyguard”), Danish livgarde (“bodyguard”), Swedish livgarde (“bodyguard”). Compare also Old English līfweard (“guardian of life”).

lifeguard (plural lifeguards)

1. (uncommon) A bodyguard or unit of bodyguards, a guard of someone's (especially a king's) life or person.
   • 1776, The London Magazine, Or, Gentleman's Monthly Intelligencer:

     "The people's love is the king's lifeguard."

   • 1843, Edward Hyde, The History of the Rebellion and Civil Wars in England, page 553:

     [I]n the reserve were the king's lifeguard, commanded by the earl of Lindsey, and prince Rupert's regiment of foot[.]

   • 2012, Charles Oman, A History of the Art of War: The Middle Ages:

     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.

2. (chiefly US) An attendant, usually an expert swimmer, employed to save swimmers in trouble or near drowning at a body of water.
3. A lifesaver.
4. (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.