- The definition of a knapsack is a bag for carrying supplies that is worn on the back.
An example of a knapsack is a schoolbag.
A woman wearing a backpack or knapsack.
knapsack definition by Webster's New World
Origin: Dutch knapzak ; from knappen (see knap) plush zak, a sack
knapsack definition by American Heritage Dictionary
Origin: Probably Low German Knappsack : knappen, to bite (probably of imitative origin) + Sack, bag (from Middle Low German sak, from Old High German sac, from Late Latin saccus; see sack1).