Thread:LilyLacreag/@comment-4850222-20130131175721

Nowhere in the book does it say that Billy's full name is William. You may write in the Etymology section that Billy is possibly a variant of Bill which is short for William. Billy itself is not short for William, but more like  a common name for something "not intelligent" which Billy happens to be. The name even sounds like what people sometimes call goats (billy goats). 