Etymology
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assure (v.)

late 14c., "reassure, give confidence to; make secure or safe, protect; bind by a pledge, give a promise or pledge (to do something)," from Old French asseurer "to reassure, calm, protect, to render sure" (12c., Modern French assurer), from Vulgar Latin *assecurar, from assimilated form of Latin ad "to" (see ad-) + securus "safe, secure" (see secure (adj.)). Related: Assured; assuring.

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reassure (v.)

also re-assure, "restore (someone) to confidence," 1590s, from re- "back, again" + assure. Related: Reassured; reassuring.

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assured (adj.)

late 14c., of persons, "confident, self-assured," past-participle adjective from assure. From early 15c. as "secure, made safe." Related: Assuredly; assuredness.

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assurance (n.)

late 14c., "formal or solemn pledge, promise," also "certainty, full confidence," from Old French asseurance "assurance, promise; truce; certainty, safety, security" (11c., Modern French assurance), from asseurer "to reassure, to render sure" (see assure). The meaning "self-confident" is from 1590s. The word had a negative tinge 18c., often suggesting impudence or presumption.

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*ad- 

Proto-Indo-European root meaning "to, near, at."

It forms all or part of: abate; ado; ad-; ad hoc; ad lib; adage; adagio; add; adjective; adore; adorn; adult; adverb; advertise; agree; aid; alloy; ally; amontillado; amount; assure; at; atone; exaggerate; paramount; rapport; twit.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit adhi "near;" Latin ad "to, toward;" Old English æt.

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ensure (v.)

late 14c., from Anglo-French enseurer, from en- "make" (see en- (1)) + Old French seur "sure" (see sure); probably influenced by Old French asseurer "assure." Compare insure. Related: Ensured; ensures; ensuring.

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insure (v.)

mid-15c., insuren, spelling variant of ensuren "to assure, give formal assurance" (late 14c.), also "make secure, make safe" (c. 1400), from Anglo-French enseurer, Old French ensurer, from en- "make" (see en- (1)) + seur, sur "safe, secure, undoubted" (see sure (adj.)).

The particular commercial senses of "make safe against loss by payment of premiums; undertake to ensure against loss, etc." are from mid-17c. (replacing assure in that meaning). Related: Insured; insuring.

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ascertain (v.)

early 15c., "to inform, to give assurance" (a sense now obsolete), from Anglo-French acerteiner, Old French acertener "to assure, certify" (13c.), from a- "to" (see ad-) + certain "sure, assured" (see certain). The meaning "find out for sure by experiment or investigation" is attested by 1794. Related: Ascertained; ascertaining.

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grant (n.)

late 14c., "something granted; authoritative bestowal of a privilege, etc.," from Anglo-French graunt, Old French graant, collateral variant of creant "promise, assurance, vow; agreement, pact; will, wish, pleasure," from creanter "be pleasing; assure, promise, guarantee; confirm, authorize" (see grant (v.)). Earlier in English in now-obsolete sense of "allowance, permission" (c. 1200). Especially "money formally granted by an authority" from c. 1800. In American English, especially of land, from c. 1700.

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compromise (n.)
Origin and meaning of compromise

early 15c., "a joint promise to abide by an arbiter's decision," from Old French compromis (13c.), from Late Latin compromissus, past participle of compromittere "to make a mutual promise" (to abide by the arbiter's decision), from com "with, together" (see com-) + promittere "to send forth; let go; foretell; assure beforehand, promise," from pro "before" (from PIE root *per- (1) "forward," hence "in front of, before") + mittere "to release, let go; send, throw" (see mission).

The sense of "a coming to terms, a settlement of differences by mutual concessions" (mid-15c.) is from extension to the settlement itself. The meaning "that which results from such an agreement" is from 1510s.

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