knap·sack (nāp'sāk') n. A bag made of sturdy material and furnished with shoulder straps, designed for carrying articles such as camping supplies on the back.
[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).]