rucksack vs back pack

rucksack and back pack both are nouns.

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

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

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

Other synonyms of rucksack include backpack, haversack, knapsack, packsack.

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