noun

• (historical, military) Any horse used in horse-cavalry, but especially one bearing an armoured knight.
  "Just within the inner edge of the circle stood a soldier, in the military attire of a strange nation; and without it was his warhorse, in the center of a collection of mounted domestics, seemingly in readiness to undertake some distant journey."
• (figurative, informal) An experienced person who has been through many battles, situations or contests; someone who has given long service.
  "Near-synonym: workhorse"
• (theater, music) A regularly revived theatrical or musical work, as with Hamlet or a Beethoven symphony, or as excerpts thereto. May imply that the work in question has become hackneyed.
  "a Wagner warhorse"