Etymology
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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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reassurance (n.)

also re-assurance, 1610s, "assurance or confirmation repeated," from reassure + -ance. Meaning "restoration of courage or confidence" is by 1875.

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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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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). Meaning "self-confident" is from 1590s. The word had a negative tinge 18c., often suggesting impudence or presumption.
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