描出看得見的輪廓
這一層就是核心畫面本身：筆真的沿著東西的邊緣走，畫完之後輪廓清楚了。
outline sharply · verb · B2
To bring out where something ends, so its shape stands out sharply from what surrounds it.
使輪廓分明
核心畫面
Picture running a pen right along the edge of something. Before you do, it blurs into the background; after you do, anyone can see where it stops and where everything else begins. Each use of define is drawing that edge — sometimes around a shape you can see, sometimes around a meaning or a job.
可以想成拿筆沿著一個東西的邊緣描一圈：描之前，它和背景糊在一起；描完之後，哪裡是它、哪裡不是它，一眼就分得出來。de…更多收起
可以想成拿筆沿著一個東西的邊緣描一圈：描之前，它和背景糊在一起；描完之後，哪裡是它、哪裡不是它，一眼就分得出來。define 的每個用法都在畫那一圈邊界——只是有時候畫的是看得見的形狀，有時候畫的是一個意思或一份職責的範圍。From the word’s history
From Latin definire 'to limit, determine, explain', from de- 'completely' + finire 'to bound, limit', from finis 'that which divides, a boundary, border, end'. It came into English in the late 14th century meaning 'to fix or establish authoritatively'. So defining something is, at root, drawing the line around it.
來自拉丁文 definire「限定、確定、說明」，由 de-（完全地）加 finire（設下界線）組成，而 finire 的源頭是 finis——「劃分開來的東西、邊界、盡頭」。英文在 14 世紀晚期借入，一開始就帶著「把範圍定下來」的意思。所以「下定義」在字源裡其實就是「畫出邊界」這件事。
Online Etymology Dictionary (etymonline.com), entry 'define (v.)'
Two branches
把範圍和意思圈清楚
同一支筆改畫在看不見的東西上：一件事的範圍、一個字的意思。邊界還是邊界，只是這次畫在概念上。
characterize fully · verb · B2
To describe something fully and clearly, saying what makes it different from other things.
界定；明確說明
原始詞典資料8 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。
defineverb/dɪˈfaɪn/
- 1
To determine with precision; to mark out with distinctness; to ascertain or exhibit clearly.
- the defining power of an optical instrument
- Rings[…]very distinct and well defined.
- 2
obsoleteTo settle, decide (an argument etc.).
- These warlike Champions, all in armour shine, / Assembled were in field the chalenge to define.
- 3
To express the essential nature of something.
- I define myself as a techno-anarchist.
- Your past mistakes do not define who you are.
- 4
To state the meaning of a word, phrase, sign, or symbol.
- The textbook defined speed as velocity divided by time.
- 5
To describe, explain, or make definite and clear; used to request the listener or other person to elaborate or explain more clearly his or her intended meaning of a word or expression.
- Person 1: Is she good at math? Person 2: Define "good." If you mean if she is faster than the average middle schooler at multiplication, then yes. If you mean if she is able to do multivariable calculus, then no.
- 6
To demark sharply the outlines or limits of an area or concept.
- to define the legal boundaries of a property
- Neither Marx nor Engels ever clearly defined the concept of class, and the last chapter of Volume III of Capital, which was to treat of this question, breaks off after three or four paragraphs.
- 7
mathematicssciencesTo establish the referent of a term or notation.
definenoun/dɪˈfaɪn/
- 1
computingengineeringmathematicsA kind of macro in source code that replaces one text string with another wherever it occurs.
- From the computer programming perspective, Java looks like C and C++ while discarding the overwhelming complexities of those languages, such as typedefs, defines, preprocessor, unions, pointers, and multiple inheritance.
- Anyone who has attempted to do OO programming in a conventional language using defines will find out that it is impossible to realize the benefits easily, if at all, without compiler support.
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。