Correct spelling, explanation: definitely is an adverb, which originated from the adjective definite complemented with suffix -ly. These two parts put together give us definitely. For that reason, the only correct spelling of this word is definitely and not definately.

Definition of definitely:
adverb: certainly, in a clear manner, with no doubt
The bus leaves in ten minutes and you are not ready! You are definitely going to be late for school again!
You look fantastic in this wedding dress, it was definitely a good choice.

Incorrect spelling, explanation: definately is the incorrect spelling of an adverb definitely. Definitely is composed of two parts, an adjective definite and suffix -ly. This is why the spelling definately is a mistaken one, and the correct version is only definitely.

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling

Incorrect spelling