surest

adjective surer, surest

1. Obsolete secure or safe
2. that will not fail; always effective: a sure method
3. that can be relied upon; trustworthy: a sure friend
4. that cannot be doubted, questioned, or disputed; absolutely true; certain
5. having or showing no doubt; positive; confident: to be sure of one's facts
6. that can be counted on to be or happen: a sure defeat
7. bound or destined to do, experience, or be something specified: sure to be elected
8. never missing; unerring: a sure aim

adverb surer, surest

1. surely; inevitably
2. certainly; indeed: an intensive, often used as an affirmative answer to questions