份量不夠：缺乏
這一支就是核心畫面的正面用法：把注意力放在「少了多少」，缺的是可以量、可以補的東西。
deficiency (lack) · noun · C1
A lack of something that is necessary, such as something in food, a quality, or a place people need.
缺乏
核心畫面
One way to hold it: something that should be there in a certain amount simply isn't — the level has fallen short of what the thing needs to work properly. Not zero, not broken; just not enough.
某樣東西「該有的份量沒到」。想像一個標著刻度的杯子，水應該到某一條線才夠用，但實際上只到半腰——差的那一截就是 de…更多收起
某樣東西「該有的份量沒到」。想像一個標著刻度的杯子，水應該到某一條線才夠用，但實際上只到半腰——差的那一截就是 deficiency。它強調的不是「壞掉」，而是「不足、短少」：本來應該有的東西缺了一塊，於是整體就運作不順。字源上 deficient 來自拉丁 dēficere「失效、短缺」（de- 離開 + facere 做），本身就帶著「掉下來、沒達到」的意味。From the word’s history
From deficient + -cy; deficient goes back to Latin dēficere 'to fail, fall short', from de- 'away' + facere 'to do, make'. The idea of falling short of a needed level is already in the root.
由 deficient 加名詞字尾 -cy 而來；deficient 追溯到拉丁文 dēficere「失效、短缺」（de-「離開」＋ facere「做」）。「沒做到、掉到標準以下」這個意思在字根裡就已經在了，所以 deficiency 現代兩個用法都繞著「達不到應有的程度」在轉。
Wiktionary (deficiency < deficient + -cy; Latin dēficientia / dēficere) — as given in the payload's attested-origins note
Two branches
該有的地方少了一塊：缺陷
同樣是「不足」，但把鏡頭從「總量差多少」移到「哪一處沒做好」——不足變成了系統裡一個具體的弱點。
deficiency (flaw) · noun · C1
A weak point or a fault in something, such as a plan, a law, or a system.
缺陷
原始詞典資料4 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。
deficiencynoun/dɪˈfɪʃənsi/
- 1
Inadequacy or incompleteness.
- The face which emerged was not reassuring.[…]. He was not a mongol but there was a deficiency of a sort there, and it was not made more pretty by a latter-day hair cut which involved eccentrically long elf-locks and oiled black curls.
- 2
An insufficiency, especially of something essential to health.
- One of academia’s deficiencies is that, though its lecture halls and graduate schools are replete with women, its higher echelons are not. Often, this is seen as a phenomenon specific to the sciences. … In fact, the disparity applies to the whole grove. Another report from 2006, by the American Association of University Professors, found the same ratio in the faculties of arts, humanities and social science, too.
- 3
geometrymathematicssciencesThe amount by which the number of double points on a curve is short of the maximum for curves of the same degree.
- 4
geometrymathematicssciencesThe codimension of a linear system in the corresponding complete linear system.
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。