Synonyms for certain

absolute, assured, categorical, clear, confident, convinced, definite, destined, determinate, determined, emphatic, fail-safe, firm, guaranteed, incontrovertible, indisputable, indubitable, infallible, irrefragable, irrefutable, known, positive, resolute, secure, sure, sure-fire, sure-fire., surefire, unambiguous, unarguable, undebatable, undeniable, undisputable, undisputed, undoubted, unequivocal, unmistakable, unquestionable