scruff vs backside

scruff and backside both are nouns.

Word	Noun	Adjective	Verb	Adverb
scruff	Yes	No	No	No
backside	Yes	No	No	No

As nouns, backside is a hypernym of scruff; that is, backside is a word with a broader meaning than scruff:

Other hypernyms of scruff include back end, rear.

scruff (noun)	backside (noun)
the back side of the neck	the fleshy part of the human body that you sit on
	the side of an object that is opposite its front