A tooth taken out of a straight edge. Old French endenter meant to cut notches into something, from dent, a tooth. Hold that picture — a clean line with a bite missing from it — and the modern uses line up: a coast with little bays, a carpet with a dip where the box stood, and a page whose straight left margin has a small bite at the start of every paragraph.
Partly Middle English indenten, to dent in (in- plus dent); partly Old French endenter, to cut notches into, from dent, a tooth, from Latin dens. Both routes end in the same picture, which is why cutting and pressing share one word.
一半來自中古英語 indenten「往裡壓出凹痕」（in- 加 dent），一半來自古法文 endenter「刻出齒狀缺口」，dent 來自拉丁文 dēns（牙齒）。兩條路線最後指向同一個畫面，所以「切出缺口」和「壓出凹痕」在英文裡共用一個字。
Wiktionary entries for indent (noun and verb), etymology sections, as supplied in this packet (source_refs kaikki:3f6f69a190036ae4:648102135 and :648110695)
Three branches
邊上被咬掉的那一口
這一組最貼近核心畫面，一個是那個缺口本身，一個是弄出缺口的動作。
noun · B2
An indent is a cut, notch or pressed-in mark that breaks a smooth edge or surface: the small bays along a coast, the bites cut into a key, the dip a heavy chair leaves in a carpet. It also names the blank space at the start of an indented line. The longer word indentation means the same thing and is used more often.
凹痕；缺口
把行首咬進去
整段文字的左邊界本來是一條直線；縮排等於在這條線上咬一個小缺口，讓讀者一眼看見新段落從哪裡開始。
verb · B2
To indent a line is to start it further in from the edge of the page than the lines around it, usually to show where a new paragraph, a quotation, or a level of a list begins. In a word processor you do it with the Tab key or the ruler; in code, the indent shows which lines belong inside a block. A hanging indent works the other way round: the first line stays out and the rest move in.
縮排
鋸齒契約留下來的訂單
這一支離「缺口」最遠，所以另外給它一個畫面。它跟核心的連結是概念上的，不是已證實的字源：可以想成從那種剪成鋸齒、可以互相核對的正式文件走過來的。
noun · C1
An indent is an official written order for goods or equipment, sent by a company, an army unit or a government office to whoever supplies them. It lists what is wanted and how much, and it has to be approved before anything is sent. You send or place an indent, and you talk about an indent for something.
訂購單；訂貨單
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。
indentnoun/ˈɪndɛnt/
A cut or notch in the margin of anything, or a recess like a notch.
A stamp; an impression.
A certificate, or intended certificate, issued by the government of the United States at the close of the Revolution, for the principal or interest of the public debt.
A requisition or order for supplies, sent to the commissariat of an army.
indentverb/ɪnˈdɛnt/
To notch; to jag; to cut into points like a row of teeth
To be cut, notched, or dented.
To dent; to stamp or to press in; to impress
historicalTo cut the two halves of a document in duplicate, using a jagged or wavy line so that each party could demonstrate that their copy was part of the original whole.
obsoleteTo enter into a binding agreement by means of such documents; to formally commit (to doing something); to contract.
obsoleteTo engage (someone), originally by means of indented contracts.
mediapublishingtypographyTo begin (a line or lines) at a greater or lesser distance from the margin. See indentation, and indention. Normal indent pushes in a line or paragraph. "Hanging indent" pulls the line out into the margin.
obsoleteTo crook or turn; to wind in and out; to zigzag.
governmentmilitarypoliticsTo make an order upon; to draw upon, as for military stores.
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。