backpack vs knapsack

backpack and knapsack both are nouns.

Word	Noun	Adjective	Verb	Adverb
backpack	Yes	No	Yes	No
knapsack	Yes	No	No	No

As nouns, backpack and knapsack are synonyms defined as:

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

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

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

backpack (verb)	knapsack (verb)
hike with a backpack