Synonyms of the word

surely

• adv. Without fail.
• adv. Certainly, undoubtedly.
• adv. With confidence.

certainly

• adv. In a way which is certain; with certainty.
• adv. Without doubt, surely.
• adv. An emphatic affirmative answer; of course.

sure

• adj. Physically secure and certain, non-failing, reliable.
• adj. Certain in one's knowledge or belief.
• adj. Certain to act or be a specified way.
• adj. (obsolete) Free from danger; safe; secure.
• adj. (obsolete) Betrothed; engaged to marry.
• adv. (modal adverb) Without doubt, certainly.
• interj. Yes. (Expresses noncommittal agreement or consent.).
• interj. Yes; of course.