purty

Purty is probably the most common American example of metathesis, a linguistic process in which two adjacent sounds are reversed in order. Metathesis in English often involves the consonant r and a vowel, since the phonetic properties of r are so vowellike. For example, the word third used to be thrid, and bird, brid. By the same process, English pretty often came to be realized as purty in regional speech. Most such words stabilized because of the influence of printing and the resultant standardized spelling, but purty for pretty has survived in regional American dialects (quote from Free Online Dictionary)