Meaning

adjective definite but not specified or identified

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

adjective established beyond doubt or question; definitely known

originFrom Middle English certeyn, certein, certain, borrowed from Old French certain, from a Vulgar Latin unattested form *certānus, extended form of Latin certus (“fixed, resolved, certain”), of the same origin as cretus, past participle of cernere (“to separate, perceive, decide”). Displaced native Middle English wis, iwis (“certain, sure”) (from Old English ġewiss (“certain, sure”)) and alternative…

Etymology from Wiktionary, CC BY-SA 3.0