Meaning

adjective having or feeling no doubt or uncertainty; confident and assured

adjective exercising or taking care great enough to bring assurance

adjective certain to occur; destined or inevitable; ; ; - Benjamin Franklin

originFrom 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”)…

Etymology from Wiktionary, CC BY-SA 3.0