From Longman Dictionary of Contemporary Englishknapsackknap‧sack /ˈnæpsæk/ noun [countable] American English DLa bag that you carry on your shoulders SYN backpack, rucksack
Examples from the Corpus
knapsack• He had a knapsack over his shoulder.• She put on her coat and hauled the new bag up on to her back like a knapsack.• In the airport she practiced with her knapsack, trying to slide it on and off.• He finished, washed the bowl, put his books in his knapsack and went outside to unlock his bike.• After a while, to Robbie's relief, Fen threw off his knapsack, suggesting they stop and eat their sandwiches.• We moved in with what we carried in our knapsacks.• He enclosed a stamped addressed envelope the size of a small knapsack.• He arrives for class with a tiny knapsack packed with his crayons, lunch box and a diaper.Origin knapsack (1600-1700) Low German knappsack or Dutch knapzak “food bag” 