Source : Webster's Revised Unabridged Dictionary (1913)

Stayer \Stay"er\, n.
   One who upholds or supports that which props; one who, or
   that which, stays, stops, or restrains; also, colloquially, a
   horse, man, etc., that has endurance, an a race.

Source : WordNet®

stayer
     n : a person or other animal having powers of endurance or
         perseverance; "the horse that won the race is a good
         stayer"