scruff (n.)
"nape of the neck," 1790, altered (by influence of scruff "crust") from scuft (1787), probably related to North Frisian skuft "back of the neck of a horse" and Dutch schoft "withers of a horse," from a common Germanic source (compare Old Norse skopt "hair of the head," Gothic skuft, Middle High German schopf, German Schopf). Another theory holds it to be a variant of scurf.