A commenter on the “non-believer epitaph” thread writes,
“Epitaph” is probably used for “epithet” more often than “epithet” is. I can’t help but wonder if it’s only a matter of time before epithet becomes an archaic word and epitaph replaces it completely.
This, I think, overestimates the frequency of the error. A quick Google search for “racial epithet,” for instance, yields 154,000 hits; “racial epitaph” yields 14,600, some of which are references to the error. Searches I’ve done with other likely adjectives gave me similar results. Maybe matters are different in speech than even in the informal writing present on the Internet, but I know of no evidence of that.
Part of the reason for such illusions, I suspect, is that erroneous usages are jarring and therefore noticeable; we therefore remember them more than we remember the correct usages. In any event, it seems that in this instance, the “epithet” / “epitaph” distinction is, at least at this point, pretty strongly maintained.