back end vs scruff

back end and scruff both are nouns.

Word	Noun	Adjective	Verb	Adverb
back end	Yes	No	No	No
scruff	Yes	No	No	No

As nouns, scruff is a hyponym of back end; that is, scruff is a word with a more specific, narrower meaning than back end:

Other hyponyms of back end include nape, nucha, rearward.

back end (noun)	scruff (noun)
the side of an object that is opposite its front	the back side of the neck