Lit. 'covered'. Word used of a knight in the phrase cum equis coopertis = with covered horse, i.e. the horse was *barded. During the reign of Edward I the vast majority of knights on the king's payroll rode armoured horses; horses described as discooperti (uncovered) were very scarce. Such men with their horses could be described as 'heavy' cavalry. -
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.