Definite
Part of speech: adjective
Definition: Having distinct limits. Free from any doubt. Designating an identified or immediately identifiable person or thing
Example sentence: Understanding does not cure evil, but it is a definite help, inasmuch as one can cope with a comprehensible darkness.
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: Change is the law of life. And those who look only to the past or present are certain to miss the future.