backside vs nape

backside and nape both are nouns.

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

As nouns, nape is a hyponym of backside; that is, nape is a word with a more specific, narrower meaning than backside:

Other hyponyms of backside include nucha, scruff, rearward.

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