"Esquire" is a social rank above gentleman and below knight. The term has the same root as "equestrian", "equerry", etc; esquires were, in the Middle Ages, men-at-arms (who fought on horseback in full plate armour), who *might* become knights through valour or service. The title in the Middle Ages usually indicates possession of sufficient estates and income to support at least one mounted man-at-arms plus retinue.