a man with a high rank in the past who was trained to fight while riding a horse.——朗文当代大辞典

With genitive, or possessive pronoun: A military servant or follower (of a king or some other specified superior); later, one devoted to the service of a lady as her attendant, or her champion in war or the tournament; hence also fig., and even applied to a woman (quot. 1600).——牛津当代大辞典  @en