Synonyms for Sure:

adj.

absolute (adjective)
conclusive, unequivocal, supreme, unqualified, utter, positive, perfect, absolute, categorical, certain, unrestricted, undeniable, consummate, unconditional, complete, unmitigated, indubitable, definite.
affirmative (adjective)
declarative, insistent, positive, certain, categorical, affirmative, predicative, definite, assertive.
aggressive (adjective)
assertive.
all (adjective)
certain.
beyond doubt (adjective)
indisputable.
beyond question (adjective)
irrefutable.
bound (adjective)
fated.
categorical (adjective)
typical, denominational, unconditional, unequivocal, flat, definite, categorical, undeniable, absolute, unqualified, indubitable, outright, certain.
certain (adjective)
irrefutable, positive, undeniable, doubtless, incontestable, steadfast, definite, trusting, indisputable, set, veritable, Irrefragable, unmistakable, decided, incontrovertible, unequivocal, clear, assured, unquestionable, certain, confident, undoubted, indubitable, absolute, decisive, convinced, patent.
certain, definite (adjective)
decided, convinced, clear, indisputable, incontrovertible, confident, incontestable, satisfied, set, steadfast, unquestionable, indubitable, firm, steady, unquestioning, unqualified, positive, undeniable, assured, doubtless, unequivocal.
foolproof (adjective)
sure-fire.
hopeful (adjective)
aspiring, desirous, expectant, faithful, eager, hopeful, optimistic, yearning.
inevitable (adjective)
certain, bound, guaranteed.
physically stable (adjective)
secure, safe, strong.
positive (adjective)
positive.
safe (adjective)
immune, safe, protected, inviolable, secure, harmless.
self-confident (adjective)
decisive.
trusting (adjective)
confident, believing, trusting, faithful.
undisputed (adjective)
undoubted.

adv

certainly (adverb)
by all means, of course, absolutely, positively, but definitely.

n.

factual, firm, definitely, objective, realistic. any, actively, e'en, bloody, even, awfully, e'er, actual, entirely, awful. admittedly, let's face it, I must confess, all-right, actually, my bad, to be sure. yes, that's right, I don't mind if I do, uh-huh, you're on, naturally. unfalteringly, satisfied, unquestioning. bright, budding, healthy, promising, feasible, rosy, sure-fire, up-and-coming. irresistible, robust, solid as a rock, sturdy, stubborn, durable, strong, tough, heavy-duty. guaranteed, probable, possibly, likely, probably, expected. not at all, no problem, it's/that's all right, it's no bother, (it's) my pleasure, sure thing, don't mention it, it's nothing/think nothing of it, you're welcome. sure (noun)
for certain, trusted, trustworthy, dependable, destined, in for, surely, indisputable, fated, foreordained, reliable, secure, predestinate, confident, doomed, trusty, careful, bound, predestined, sure as shooting, certain, positive, true, steady, convinced, certainly, for sure.

Other synonyms:

expected, feasible, budding, admittedly, probably, objective, unquestioning, uh-huh, promising, satisfied, sure-fire, up-and-coming. likely, guaranteed, probable, naturally. healthy, sturdy, rosy, of course, yes, bright. positively, actually, possibly. all-right. strong. fated
fated.
Other relevant words:
destined, for sure, doomed, up-and-coming, unquestioning, to be sure, no problem, predestined, possibly, positively, tough, foreordained, sure-fire, fated, satisfied, certainly, careful, for certain, reliable, trusty, sure thing, strong, firm, actually, of course, steady, trustworthy, probable, sure as shooting, trusted, by all means, healthy, sturdy, definitely, budding, in for, durable, guaranteed, yes, expected, predestinate, bright, true, dependable, factual, bound, likely, naturally, irresistible, even, admittedly, surely, uh-huh, absolutely.

Usage examples for sure

  1. I am sure they would. – Charlotte's Inheritance by M. E. Braddon
  2. It's sure to be all right. – Bird of Paradise by Ada Leverson
  3. But I am sure you will. – Ralph the Heir by Anthony Trollope