Certain
Part of speech: determiner
Definition: Having been determined but unspecified. The quality of some particular subject or object which is known by the speaker to have been specifically singled out among similar entities of its class.
Part of speech: adjective
Definition: Sure, positive, not doubting.
Example sentence: Our greatest weakness lies in giving up. The most certain way to succeed is always to try just one more time.
Confident
Part of speech: adjective
Definition: being very sure of or positive about somethingself-confident
Example sentence: When I pay attention to the little details, such as matching accessories to the entire outfit, I only get more confident on stage.