Our word of the day, wax, reminded Dr. Orrin Davis of a story he once heard about the word sincere, which he shared with me today:
“Evidently, high quality marble has been a favorite kitchen and building material for a long, long time. The highest quality marble, I was told, has few holes. Cheaper marble has many holes and crevices. Therefore, in order to make poor quality, or ‘holey’ marble appear better, the defects were filled with wax, a.k.a [Latin] cere. To be good marble, the stone was ‘without wax’ or ‘sin cere’. With wax was ‘insincere’.”
Actually, the most wide-spread story is that Roman potters would fill cracks in defective pots with wax the same color as the pot and sell the pots as perfect. To convince a customer that a pot was perfect, the potter had to convince him that it was sin cera “without wax”. That has long been established as either an urban myth (or an old wives’ tale, depending on your age and slang generation). Of course, sincere does not mean “without wax” or even “perfect” so the semantic side of this proposed derivation never worked.
Sincere comes to English from Latin sincerus “sound, whole, pure, genuine” via French. Its origin is simply unknown. A possible source would be a Proto-Indo-European compound sem-kero-s “of one growth” based on sem- “same, one” + kero- “to grow”. Although semantics troubles this purely speculative derivation, too, I sincerely believe it is the most likely historical scenario for the development of sincere.