(idiomatic) Certainly, undoubtedly, admittedly.

Without fail. / Certainly, undoubtedly. / With confidence.

definitely, positively, without doubt

Physically secure and certain, non-failing, reliable. / Certain in one's knowledge or belief. / (followed by a to infinitive) Certain to act or be a specified way.

(modal adverb) Without doubt, certainly. / (archaic) Without fail, surely.

Yes, expressing noncommittal agreement or consent. / Yes; of course. / You're welcome; polite response to being thanked.

(uncountable) The property of being sure, certainty. / (uncountable) The property of being sure, deft, confident of ability. / (countable, rare) The result or product of being sure.

plural of sureness

(simile) Most certainly; definitely.

(simile) Absolutely certain.