“Definitely” is the correct spelling of the word.
“Definately” is incorrect and should not be used in English.
The word “definitely” means “without doubt” or “certainly”.
I definitely want to go see the new Spiderman movie in the cinema.
Do you want to go for ice cream?
All of the words above are misspellings of “definitely” and should not be used when you want to use “definitely”,
“Defiantly” has a different meaning and means to show pride in obeying an authority.
How to remember how to spell “Definitely”
I must admit that I also have difficulty remembering how to spell “Definitely” and I am not alone as it regularly comes up as one of the most difficult words in the English language.
The way that I remember it is that it is double “i” as in “definitely” because most people misspell the word as “Definately” because that is how it sounds when it is spoken.