In the fifteenth and sixteenth centuries the petticoat was a garment that was actually, as the name indicates, a “little coat.”
At first it was a man’s coat, worn under his armor as a protection against chafing.
Later he wore it as an undergarment beneath his doublet, as a waistcoat or sort of vest. And it was thus, then, that women first wore it, as a sort of chemise.
But in the seventeenth century women began to extend the name to the underskirt appended from the chemise, or, as at present, to any underskirt.