metathesis

One familiar example of metathesis is the English word thrill, which was thyrlian in Old English and thirlen in Middle English. By the late 16th century, native English speakers had switched the placement of the r to form thrill. Another example is the alteration of curd into crud (the earliest sense of which was, unsurprisingly, curd). It probably won't surprise you to learn that the origin of metathesis lies in the idea of transposition—the word was borrowed into English in the mid-16th century and derives via Late Latin from the Greek verb metatithenai, meaning "to transpose."