back pack vs backpack

back pack and backpack both are nouns.

Word	Noun	Adjective	Verb	Adverb
back pack	Yes	No	No	No
backpack	Yes	No	Yes	No

As nouns, back pack and backpack are synonyms defined as:

back pack and backpack: a bag carried by a strap on your back or shoulder

Other synonyms of back pack include haversack, knapsack, packsack, rucksack.

back pack (noun)	backpack (noun)
a bag carried by a strap on your back or shoulder	a bag carried by a strap on your back or shoulder

back pack (verb)	backpack (verb)
	hike with a backpack