scruff

1. the back of a person's or animal's neck.

   he grabbed him by the scruff of his neck

verb

grasp (an animal) by the scruff of its neck.

late 18th century: alteration of dialect scuff, of obscure origin.

1. a person with a dirty or untidy appearance.
2. short, bristly hairs growing on a man's face when he has not shaved for a while; stubble.

   several days' worth of scruff

early 16th century (in the sense ‘scurf’): variant of scurf. The word came to mean ‘worthless thing’, whence scruff² (sense 1) (mid 19th century).