The word “sincere” was often thought to derive from the Latin “sine cera” or “without wax” and was thought to refer to the adulteration of marble by unscrupulous Romans. Hence Ezra Pound, “We have a word ‘sincere’, said to date from the Roman luxury trade in fake marble” (“Confucius and Mencius,” Selected Prose: 1909-1965, [New York: New Directions, 1973]: 84). The OED notes that this has “no probability,” but it’s easy enough to see why it appealed to Pound, who was very concerned about the adulteration of all things in the present age.
I can’t remember if I did this in a class one time, or if I was just thinking aloud, but I remember speculating that “sincere” meant “without corn,” with “corn” having something like the American-derived meaning of sentimental or hackneyed (said to derive from seed catalogue jokes of the late 19th C). That the original meaning would then be somewhat contrary to the present meaning of the word I counted in anachronistic favor.
The “new sincerity” seems first to have applied to some Austin-area bands, I just learned. One of them, now called The Reivers, after a choral group objected to them also calling themselves Zeitgeist. About their album, Translate Slowly (1985), Robert Christgau observed, “There’s hope, though–if they get picked up by Elektra and break through on a fluke video, they may start writing about cocaine and Holiday Inns.”