Learn English – the difference between “definite” and “definitive”

thefreedictionary actually explains the difference under "definite":

Usage: Definite and definitive should be carefully distinguished. Definite indicates precision and firmness, as in a definite decision. Definitive includes these senses but also indicates conclusiveness. A definite answer indicates a clear and firm answer to a particular question; a definitive answer implies an authoritative resolution of a complex question.

I was writing a very similar description and example but I think this is worded better and more precisely accurate.

You might say that an answer I wrote would be definite, but the dictionary's is definitive.

The distinction has more to do with certainty.

A field has a definite boundary if the boundary is well-marked, perhaps with a fence. But maybe the farmer made a mistake and put the fence a few feet away from where his property actually ends; it's still definite because it's clearly marked. The boundary could be said to be definitive if it was outlined and set in a manner that made its position correct beyond question.

A lower court's ruling is definite because it is clearly put forth, but the Supreme Court's rulings are also definitive because they are the final word on the subject.