1.border指兩個國家或區域間的分界，或邊界地區，邊境。
border disputes 邊境爭端
Our car was turned back at the border.
我們的汽車在邊境被擋了回來。
They didn't reach the border until after dark.
他們天黑以後才到達邊境。
He was arrested by guards at the border crossing.
他在邊境過境處被衛兵逮捕。
The border will be policed by UN officials.
邊境將由聯合國官員巡查。
Any day now, the Northern forces may pour across the new border.
北方的軍隊現在隨時都可能大批越過新邊界。
When did the country open its borders?
這個國家是何時開放邊界的？
At least 5 000 missiles were deployed along the border.
沿邊境至少部署了5000枚飛彈。
Guards have been posted along the border.
邊界上已部署了邊防崗哨。
The UN has undertaken to reinforce its military presence along the borders.
聯合國已經著手增援其駐紮在邊境的軍事力量。
Renewed fighting has been reported on the border.
據報導，在邊境地區戰火重燃。
Troops patrolled the border day and night.
軍隊日夜在邊境地區巡邏。
The border dispute turned into a full-blown crisis.
邊境爭端已演變成全面危機。
It is difficult to define the border between love and friendship.
愛情和友情之間的界線難以劃清。
2.boundary指兩個地區間最外邊的界線，分界線，邊界線，是地理概念，可作比喻意義。
boundary亦可指兩地間的分界線，如用籬笆或牆隔開的分屬於不同的兩個人的土地分界線：
the boundary fence/wall between the properties
地產間的籬笆 / 牆分界線
national boundaries 國界
A river forms the boundary between the two countries. 一條河形成了兩國間的分界線。
The fence marked the boundary between my property and hers.
那道籬笆曾是我和她的房產之間的地界。
Scientists continue to push back the boundaries of human knowledge.
科學家不斷擴大人類知識的範圍。
the boundaries of human knowledge 人類知識的範圍
地圖上標示的國界線可叫boundary，但穿越國界不用boundary：
After the war the national boundaries were redrawn.
戰後重新劃定了國界。
在英國，boundary既指地圖上標示的郡界，也指地面上的郡界：
We crossed the county boundary into Devon.
我們越過郡界進入了德文。
states and counties in the US are separated by lines but 『line』 is not used for national borders.
在美國，州界和縣界用line，但國界不用line：
crossing state/county lines
跨越州界 / 縣界
The boundaries between history and storytelling are always being blurred and muddled.
歷史和軼聞的分界向來是模糊而混亂的。
3.frontier指國家邊境地區，不指州、省、縣、市等界限。指國界、邊界、邊疆、邊境：
The river formed the frontier between the land of the Saxons and that of the Danes.
這條河曾是撒克遜人與古斯堪地那維亞人土地的分界線。
They tried to cross the frontier. 他們試圖越過國界。
國界線通常叫border；英國英語亦可叫frontier，但frontier常與荒蕪、危險和不確定聯繫在一起：
The rebels control the frontier and the surrounding area.
叛亂分子控制了邊疆地區。
4.bounds（用複數）指界限範圍，大小由人為因素而定，用於比喻意義可以指人的行為界限。指事情的極限或可以接受的範圍，常用於比喻
This place is out of bounds to school children. 這個地方不准小學生入內。
Public spending must be kept within reasonable bounds.
公共開支必須控制在合理的範圍內。
It was not beyond the bounds of possibility that they would meet again one day.
他們有一天會再度相遇，這不是沒有可能。
It is not beyond the bounds of possibility that we'll all meet again one day.
我們大家將來有一天再度聚在一起，並非絕不可能。
His shot went out of bounds.
他的球出界了。
His enthusiasm knew no bounds (= was very great) .
他有無限熱情。
His demands were out of bounds.
他的要求不合理。
It's beyond the bounds of my ability.
這超出了我的能力範圍。
Knowledge knows no bounds.
知識是沒有窮盡的。
5.line指假想的或地圖上標示的兩地間的分界線、邊界線：線;（行進的）方向，路線;方法;生產線;管道;線條;排;軌道;行業;界線;防線;台詞，對白;分界線;（人）隊伍，行列;電話線路;邊線;種類;皺紋;態度，看法;話，言語;運輸公司;字行;褶子;(尤指運動場地的)場地線，場界;一段繩（或索、線等）;按時間順序排列的人（或物、事件）；（思想或行為等的）界限，界線
lines of longitude and latitude
經線和緯線
Draw a thick black line across the page.
在此頁上橫畫一條粗黑線。
Be careful not to cross the line (= the broken line painted down the middle of the road).
小心別越過道路的中界線。
Your feet must be behind the line when you serve (= in tennis ) .
發球時你的腳必須站在底線的外面。
They were all waiting on the starting line.
他們全都在起跑線上等待著。
He traced the line of her jaw with his finger.
他用手指順著她的下巴外緣撫摸。
They were stuck in a line of traffic.
他們塞在汽車長龍裡面了。
Orders came down the line from the very top.
命令從最高領導人逐級傳達下來。
I can only remember the first two lines of that song.
我只記得那首歌的頭兩句歌詞。
Drop me a line when you get there.
你到那兒後給我寫封信。
I could see the finish line and thought I was home and dry.
我能看見終點線了，我想我終於成功了。
Their aim was to block guerrilla supply lines.
他們的目的是封鎖游擊隊的供給線。
Their unit was shelling the German lines only seven miles away.
他們的部隊在炮轟僅有7英里之遙的德軍防線。
He was convicted of illegally importing weapons across state lines.
他被判犯有非法越境偷運武器罪。
We want to cut across lines of race, sex and religion.
我們要超越種族、性別和宗教的界限。
The bottom line is that we have to make a decision today.
底線是，我們今天必須作出決定。
It is, however, not possible to draw a distinct line between the two categories.
不過，這兩個類別無法涇渭分明地區分開來。