Definite (adjective) or definitely (adverb) means certain, without a single doubt:

We have definite plans to move to New York.

(it is 100% certain that we will move there)

I'm definitely going to the party.

(it is 100% certain that I am going)

This $50 jacket is definitely overpriced. I saw the exact same jacket for $30 in another store.

(it is completely certain that $50 is too much)

The word definitively (adverb) or definitive (adjective) means that something decides an issue, or provides a clear and firm answer/solution to a particular matter:

The evidence from the DNA test definitively proved that Ryan was not the murderer.

The company had been in financial trouble for years, but its definitive end came when it declared bankruptcy in March.

Things Psychology Tells You About Yourself

Most of your decisions are subconscious

Although you like to think that all of your decisions are carefully controlled and thought out, research tells us that most of our everyday decisions are actually subconscious. There is a reason for this though. Every second our brains are bombarded with over 11 millions individual pieces of data and because there is no way we can consciously sift through all of it our subconscious mind, following certain rules of thumb, helps us out.