There is a lovely story that “sincere” comes from the Latin sine cera, without wax: crooked sculptors filled the cracks in their marble with wax, and an honest one sold you stone with nothing hidden. It turns up in sermons and wedding speeches, and there is no evidence for it at all. No Roman writer uses the phrase, and nobody has found the wax-filling marble sellers; the word seems to come from sincerus, clean or unmixed, and past that the trail goes cold. So the best-loved explanation of the word for having nothing filled in is itself a crack in the record, smoothed over with something that looks like stone. I find I don’t mind. It’s a fake that happens to be a perfect example of the thing it warns you about.