Correct spelling, explanation: pretty is a word that evolved from Old English prættig, prettī through Middle English pratte, prettie to the current form pretty. That means that the version preety is not correct and is a misspelling because the wrong letter was doubled. The primary function of pretty is as an adjective, but it can also be an adverb, however, it does not change the spelling.

Definition of pretty:
adjective: about people, but also other things; something pleasant to look at, attractive, delicate;
She used to be very pretty when she was a young girl, with her blue eyes and shiny blond hair.
adverb (informal): quite, very, to some degree;
I am pretty sure she lied she was sick to avoid the exam.

Idioms with pretty:
cost sb a pretty penny: be very expensive;
Look at that car! It must have cost you a pretty penny.
not be just a pretty face: someone who is not only attractive but also intelligent;
When she won an important academic grant, she proved that she is not just a pretty face.
not be a pretty sight: something or someone ugly, unpleasant to look at;
After giving birth, I was very tired and focused on the baby, so trust me it was not a pretty sight.
sitting pretty: be in an advantageous position;
If I get that job, I will be sitting pretty in the safe corporate office.

Incorrect spelling, explanation: preety is a misspelled version of the word pretty. Pretty comes from Old English times when it was spelled as prættig, prettī, then in Middle English, it evolved to pratte, prettie. Today’s spelling is quite similar because we still have the double letter t. For that reason, the spelling preety is incorrect.

Incorrect spelling

Incorrect spelling