The full modern name is The Most Honourable Order of the Bath; but in the Middle Ages it was not a formal order of knighthood. The name represents a relic of the rituals attendant on the conferring of a knighthood. After a night of vigil in a church, the candidate took a purifying bath before he heard mass. Dubbing knights at a state occasion was common in Henry V's reign. The order fell out of fashion until the early 18c, when it was revived by the then *Garter King of Arms.
Dictionary of Medieval Terms and Phrases. Christopher Coredon with Ann Williams.