Etymology
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indent (v.2)
"to dent or press in," c. 1400, from in (adv.) + dent (v.). Etymologically distinct from indent (v.1) but felt as the same.
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indent (n.)

"cut or notch in a margin," 1590s, from indent (v.1). A supposed earlier noun sense of "a written agreement" (late 15c.) is described in The Middle English Compendium as "scribal abbrev. of endenture."

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indent (v.1)

early 15c., indenten, endenten "to make notches; to give (something) a toothed or jagged appearance," also "to make a legal indenture, make a written formal agreement or contract," from Old French endenter "to notch or dent, give a serrated edge to" (12c.) and directly from Medieval Latin indentare "to furnish with teeth," from in- "into, in, on, upon" (from PIE root *en "in") + verb from Latin dens (genitive dentis) "tooth" (from PIE root *dent- "tooth").

An indented document was usually, if not always, written in two or more identical versions. Orig. these were written on a single sheet of parchment and then cut apart along a zigzag, or 'indented' line. Each party to the agreement retained one copy, which he could readily authenticate by matching its serrate edge with that of another copy. [Middle English Compendium]

The printing sense "insert white space to force text inward" is first attested 1670s. Related: Indented (late 14c.); indenting.

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indentation (n.1)
"cut, notch, incision," 1728, of margins or edges, extended form of indent (n.).
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indentation (n.2)
"action of making a dent or impression; small hollow or depression, slight pit," 1847, from indent (v.2).
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indention (n.)
1763, formed irregularly from indent (v.1). It could be a useful word if it split with indentation the two senses (relating to marginal notches and to dents) of that word, but indention, too, is used in both.
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dent (n.)

early 14c., "a strike or blow," dialectal variant of Middle English dint, dunt (see dint); sense of "indentation, hollow mark made by a blow or pressure" is by 1560s, apparently by influence of indent.

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indenture (n.)
late 14c., endenture, indenture, "written formal contract for services (between master and apprentice, etc.), a deed with mutual covenants," from Anglo-French endenture, Old French endenteure "indentation," from endenter "to notch or dent" (see indent (v.1)).

Such contracts (especially between master craftsmen and apprentices) were written in full identical versions on a sheet of parchment, which was then cut apart in a zigzag, or "notched" line. Each party took one, and the genuineness of a document of indenture could be proved by laying it beside its counterpart.
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*dent- 

Proto-Indo-European root meaning "tooth."

It forms all or part of: al dente; dandelion; dental; dentifrice; dentist; dentition; denture; glyptodon; indent (v.1) "to make notches;" mastodon; orthodontia; periodontal; teethe; tooth; toothsome; tusk; trident.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit danta, Greek odontos (gen.), Latin dens, Lithuanian dantis, Old Irish det, Welsh dent, Old English toð, German Zahn, Gothic tunþus "tooth."

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impress (v.1)

late 14c., "have a strong effect on the mind or heart, to stamp deeply in the mind," from Latin impressus, past participle of imprimere "press into or upon, stamp," also figurative, from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + premere "to press, hold fast, cover, crowd, compress" (from PIE root *per- (4) "to strike"). Literal sense of "to apply with pressure, make a permanent image in, indent, imprint" is from early 15c. in English. Related: Impressed; impressing.

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