The Rice University Neologisms Database

Definition: a person (usually female) who has an attractive body but an unattractive face... the word is a triple contraction of but-her-face. Butterface: It is a compound word and a type of sound combination because “but her” sounds like butter if said quickly. It is also a type of euphemism because it is a way of calling someone ugly without using a word with a mean connotation. Origin: I heard it used for the first time at my job in July of 2005. It could possibly have begun as Australian slang earlier than that and come across to the U.S. more recently.