back pack vs rucksack

back pack and rucksack both are nouns.

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

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

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

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

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