- 1眾所周知的、有名的（比 famous 溫和、範圍可大可小，也可說「在某圈子裡很有名」）
Well-known means a lot of people know it — a person, a place, a fact, a shop, a song. It works two ways that are worth separating. About people and things, it is close to famous but calmer and smaller in scale: a well-known author is known to readers, a famous author is known to everyone. It also takes a boundary very naturally — "well-known in ", "well-known among doctors" — which famous resists. About facts, it means everybody already knows this, so I am not going to argue for it: "it is well-known that sleep affects memory". Writers lean on that phrase, sometimes to slip an claim past you, so it is worth reading with a raised . It is neutral about good and bad — you can be well-known for kindness or for cheating — though when the reason is bad, English often prefers notorious. Before a noun it takes a ; after be, both "well known" and "well-known" are written, and either is accepted. The comparative is better-known / best-known, not "more well-known", which sounds wrong to native ears even though you will hear it.
well-known 指很多人知道的人、地方、事實、店家或歌曲。它跟 famous 很接近，但比較溫和、範圍可大可小：一位 well-known 的作家是讀者認識，famous 的作家則是大家都認識。它很自然地可以加上範圍，例如「well-known in Taipei」（在台北很有名）、「well-known among doctors」（在醫生之間很有名）。這類「well-known in ＿＿」的句型常用在介紹範圍的時候。
談事實時，well-known 的意思是大家早就知道，不必再爭論，例如「it is well-known that…」（眾所周知……）。作者有時會用這個句型，把沒有證實的說法帶過去，讀的時候可以多留意。它對好壞沒有立場，名聲不好時英文通常會換成「notorious」。放在名詞前要加連字號，比較級常見的是「better-known」和「best-known」。
From the word’s history
From Middle English well knowen; well + known.
源自中古英文 well knowen，由 well 和 known 組成。
組成well + known, the past participle of know. It goes back to Middle English well knowen — the two words have been travelling together for a very long time.
原始詞典資料2 筆記錄
以下是外部詞典記錄的用法，摘錄並精簡格式，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。
well-knownadj/ˌwɛlˈnoʊn/
- 1
Familiar, famous, renowned, noted or widely known.
- Edward Churchill still attended to his work in a hopeless mechanical manner like a sleep-walker who walks safely on a well-known round. But his Roman collar galled him, his cossack stifled him, his biretta was as uncomfortable as a merry-andrew's cap and bells.
- There are a number of diseases that are considered to be universally fatal. AIDS and rabies encephalitis are well-known examples.
- 2
computingengineeringmathematicsGenerally recognized; reserved for some usual purpose.
- We would like to catalog other sockets which are supposed to be well-known
- If the call to this function fails, you can assume the SID was invalid — even if it's a well-known SID.
摘錄自 英文維基詞典 English Wiktionary，已精簡格式；依 CC BY-SA 4.0 授權使用，改動後的內容同樣以此授權提供。