Correct spelling, explanation: this form is an adverbial form from the adjective definite, which is spelled with i, not e, hence the spelling definitely. The core word comes from Latin, and it is also spelled with i (definire), so definetely is the wrong form.

Definition of definitely:
adverb, in a definite, unchangeable way; of course
You should definitely buy this blouse, it looks amazing.
I am definitely going to fail this test.

Incorrect spelling, explanation: definetely is a misspelling, because we spell this word with i, just like its Latin origin: definire. Therefore the correct spelling is definitely. This adverb comes from an adjective definite, which is also spelled with i instead of e.

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling