In olden days, after ladies had their hair styled by a servant, they would have a servant fill a bellows with powder to powder it.

To contain the powder, there was often a small room set outside for this called the Powder Room.  Thus, the name of the powder room came into being.

VINEGAR OF THE FOUR THIEVES: Recipes & curious tips from the past

Check out genealogy books and novels by Donna R. Causey