地上的界線：國土與土地
這一族就是核心畫面本身：可以走過去、可以在地圖上指出來的那條實際分界。
boundary (border line) · noun · C1
The real or imagined line that marks the edge of a country, a city, or a piece of land that belongs to someone.
邊界
核心畫面
One way to picture it: a line drawn on the ground that says "this side is one thing, that side is another" — the edge where what belongs to you stops and what belongs to someone else begins.
地上畫著一條線，線的這一邊是這塊地、那一邊是另一塊地。boundary 不是「牆」，牆是實體擋住你的東西；bound…更多收起
地上畫著一條線，線的這一邊是這塊地、那一邊是另一塊地。boundary 不是「牆」，牆是實體擋住你的東西；boundary 是那條「分界」本身——它可能是一道籬笆、一條河，也可能只是地圖上的一筆，重點在於它宣告「到這裡為止」。它同時做兩件事：把裡面的框起來，也把外面的擋在外面。From the word’s history
From bound ("a limit, the furthest point something reaches") + -ary; the word is literally "the thing that has to do with the limit".
boundary 是 bound（界限、到頭的那一點）加上名詞字尾 -ary 造出來的，字面就是「跟界限有關的那個東西」，所以它天生指的就是「到頭為止的那條線」，而不是線圍起來的地。這個 bound 跟「跳」的 bound 沒關係，也跟 be bound to 的「被綁住」不同源。
Wiktionary etymology tree supplied in the payload (English bound + -ary), which also notes it displaced native Old English mearc.
Four branches
看不見的界線：可接受的範圍
從土地的分界隱喻到行為與能力的分界——一樣是「到這裡為止」，只是這條線不畫在地上，而是畫在人們的共識或現實的極限上。
boundary of acceptability · noun · C1
The limit of what people accept as all right, or of what they think is possible.
界限
概念之間的交界
同樣是「到這裡為止」，但兩邊不是土地、也不是行為，而是兩種說不太清楚的東西——感覺、性質、學科；線畫在它們之間，通常還是模糊的。
boundary (dividing point) · noun · C1
The point where one feeling, idea, or quality stops and another starts.
界線
板球場的邊線
回到最具體的那條線——只是這次畫在球場上，而且因為球越過它會算分，這個字連「那一擊」本身都一併指了。
boundary (cricket) · noun · C1
In cricket, the outer edge of the playing area, or a hit that sends the ball across this edge for extra points.
邊界（板球）
原始詞典資料6 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。
boundarynoun/ˈbaʊndɹi/
- 1
The dividing line or location between two areas.
- So this was my future home, I thought![…]Backed by towering hills, the but faintly discernible purple line of the French boundary off to the southwest, a sky of palest Gobelin flecked with fat, fleecy little clouds, it in truth looked a dear little city; the city of one's dreams.
- City or national boundaries are locations of economic opportunity, especially if the existence of the border is itself the source of a monopoly situation that favors one side over the other (Krakover, 1997).
- 2
The bounds, confines, or limits between immaterial things (such as one’s comfort zone, privacy, or professional sphere and the realm beyond).
- I didn’t mean to push the boundaries by sending my boss a message on Saturday night.
- 3
ball-gamescricketgamesAn edge or line marking an edge of the playing field.
- 4
ball-gamescricketgamesAn event whereby the ball is struck and either touches or passes over a boundary (with or without bouncing), usually resulting in an award of 4 (four) or 6 (six) runs respectively for the batting team.
- Travis hit a boundary to seal the match on the last ball of the over.
- 5
mathematicssciencestopology(of a set) The set of points in the closure of a set S, not belonging to the interior of that set.
- 6
Commission paid by a bus or jeepney driver to a public transportation operator for taking passengers, or the excess collected fares taken as daily wage.
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。