Noah Webster's New International Dictionary of the English Language
1. (superl.) Certainly knowing and believing; confident beyond doubt; implicitly trusting; unquestioning; positive.
2. (superl.) Certain to find or retain; as, to be sure of game; to be sure of success; to be sure of life or health.
3. (superl.) Fit or worthy to be depended on; certain not to fail or disappoint expectation; unfailing; strong; permanent; enduring.
4. (superl.) Betrothed; engaged to marry.
5. (superl.) Free from danger; safe; secure.
6. (adv.) In a sure manner; safely; certainly.