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A fortress is a large, strong building — or a whole set of walls and towers — built to defend an important place. A castle can be a fortress, but fortress is about defence first: thick walls, a high place, soldiers inside. People also stretch the word: her home felt like a fortress means a place that is very hard to get into, not a real fort. There is an old verb to fortress, meaning to protect a place as if it were a fort, but you will almost never hear it now; the noun is the word that lives.
要塞、堡壘（比「城堡」更強調防守，不是童話裡的城堡）
組成From Old French forteresse, a strong place, from Medieval Latin fortalitia, from Latin fortis, strong, plus an ending that turns an adjective into a noun. That French ending -ess (from Latin -itia) is the same kind you hear in duress and prowess.
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。
fortressnoun/ˈfoɹ.tɹɪs/
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A fortified place; a large and permanent fortification, sometimes including a town; for example a fort, a castle; a stronghold; a place of defense or security.
- Like the Mesolithic age of 10,000-8000 B.C., the period 6000-4000 B.C. seems to be one of the fall of fortresses and the rise of pastoral nomadism.
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board-gameschessgamesA position that, if obtained by the weaker side, will prevent penetration by the opposing side, generally achieving a draw.
fortressverb/ˈfoɹ.tɹɪs/
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To furnish with a fortress or with fortresses; to guard, to fortify.
- Honour and Beautie in the owners armes, / Are weaklie fortreſt from a world of harmes.
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。