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A knapsack is a bag you carry on your back, with straps over your shoulders. Today most people say backpack, especially for school. Knapsack sounds a little older, or a little more like camping, hiking, or an old army bag. In some books, and in some British writing, you will still meet it. Though actually, the first knapsacks were bags for food on the road, not for school books. The idea was a sack for eating on a journey. Now it just means the bag on your back, food or not. There is an old verb too (to travel with a knapsack), but almost only need the noun.
背包（較舊的說法；現在比較常說 backpack）
組成From Low German or Dutch knapzak (older cnapsack): knappen, “to bite / to eat” — a sound-word — + sack, “bag.” German Knappsack came from Dutch, not the other way around.
同家族的字
- sackthe “bag” half of the old Dutch word
原始詞典資料3 筆記錄
以下是外部詞典記錄的用法，原文照列，我們還沒有寫成教學內容。上面的說明才是我們自己寫的；有些用法可能上面已經講過了。
knapsacknoun/ˈnæpsæk/
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archaicA case of canvas or leather, for carrying items on the back.
- 1936, Arthur Ransome, Pigeon Post, ch 3. "All but Nancy carried knapsacks, with sandwiches and thermos flasks of tea. Peggy’s knapsack held Nancy’s provisions as well as her own, for on Nancy’s shoulders, instead of a knapsack, was a pigeon-basket […]"
- The two elder reluctantly left him and walked on, taking their brother's knapsack to relieve him in following, and the youngest entered the field.
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computingcryptographyengineeringA set of values from which a subset is chosen.
knapsackverb/ˈnæpsæk/
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To go hiking while burdened with a knapsack, usually overnight or for longer.
- My sleeping bag fell off my backpack into the water, while we were knapsacking up the mountain.
資料來源：英文維基詞典 English Wiktionary（CC BY-SA 4.0）。 原文照列，未經改寫。