Correct spelling, explanation: pretty is a very popular word in English and in fact, it also has a very long history as it already appeared in Old English, but back then it had the form of prættig. Moreover, in the past, pretty used to mean nice, canny, or fine. Pretty was also used in the Dutch language, in which it looked as pertich or prettig. In modern English pretty functions as an adverb or as an adjective.

Definition of pretty:
1. adjective – attractive, beautiful, nice;
You’re wearing such a pretty dress today that everybody is staring at you.
2. adverb – quite;
I’m pretty sure that I saw her with another man at the club yesterday.

Phrases and expressions with pretty:
A few common phrases with pretty are: pretty good, pretty awful, and pretty soon.
The team played a pretty good game, but still, they didn’t manage to win.
Telling him that his wife is cheating on him was pretty awful, but I just had to do it.
Put the chicken into the oven, darling, as our guests will be here pretty soon.

Incorrect spelling, explanation: due to its pronunciation pretty is often misspelled as both native users of English and its learners wrongly assume that the word features only one -t letter. Consequently, they spell the word as prety instead of pretty. Remember, though, that the only correct spelling is with a double -t letter.

Incorrect spelling

Incorrect spelling