My farrier retired.  For years I spelled it ferrier, because it comes from the Latin word for iron.  They put up with me but I finally admitted my mistake. 

Wikipedia says for ferrier, "Not to be confused with farrier, a profession that specializes in hoof care (notably horseshoes)."

And Merriam-Webster online says a ferrier is a ferryman.  Like, women don't know how to cross rivers?  Or, it's an obsolete spelling of farrier.