Why is definitely so hard to spell?

Answer 1

It is no harder to spell than "definite" or "finite."

The difficulty may be that it differs from the main verb, (define) and may be mispronounced as if it had an A in it.

Answer 2

"Definitely" is often considered hard to spell because it has many letters and the placement of vowels can be confusing. Additionally, the pronunciation does not always match the way it looks, which can make it even more challenging to spell correctly.