Sure
Middle English: from Old French sur, from Latin securus ‘free from care’.
wiktionary
From Middle English sure, seur, sur, from Middle French sur or Old French seür, from Latin sēcūrus(“secure”, literally “carefree”), from sē-(“apart”) + cūra(“care”) (compare Old English orsorg(“carefree”), from or-(“without”) + sorg(“care”)). See cure. Doublet of secure and the now obsolete or dialectal sicker(“certain, safe”).
Displaced native Middle English wis, iwis(“certain, sure”) (from Old English ġewis, ġewiss(“certain, sure”)), Middle English siker(“sure, secure”) (from Old English sicor(“secure, sure”)) with which was cognate.
This etymology is incomplete. You can help Wiktionary by elaborating on the origins of this term.
etymonline
sure (adj.)
early 13c., "safe against attack, secure," later "firm, reliable" (c. 1300); "mentally certain, confident" (mid-14c.); "firm, strong, resolute" (c. 1400), from Old French seur, sur "safe, secure; undoubted, dependable, trustworthy" (12c.), from Latin securus "free from care, untroubled, heedless, safe" (see secure (adj.)). Pronunciation development is that of sugar (n.).
As an affirmative meaning "yes, certainly" it dates from 1803, from Middle English meanings "firmly established; having no doubt," and phrases like to be sure (1650s), sure enough (1540s), and for sure (1580s). The use as an adverb meaning "assuredly" goes back to early 14c. Sure-footed is from 1630s, literal and figurative; sure thing dates from 1836. In 16c.-17c., Suresby was an appellation for a person to be depended upon (see rudesby).
