also pig-tail, 1680s, "tobacco in a twisted roll," from pig (n.1) + tail (n.). So called from resemblance. Meaning "braid of hair hanging down the back of the head" is from 1753, when it was a fashion in polite society; the style was preserved into early 19c. by soldiers and sailors. Since applied variously to other objects or parts thought to resemble this in appearance. Related: Pigtailed.