a heavily armed and mounted soldier in medieval times
Man-at-arms (also called armsman or coistrel) was a term used from the High Medieval to Renaissance periods to describe a soldier, almost always a professional warrior in the sense of being well-trained in the use of arms, who served as a fully armoured heavy cavalryman. It could refer to knights or noblemen, and to members of their retinues or to mercenaries in companies under captains.