platitude (n.)
1812, "dullness," from French platitude "flatness, vapidness" (late 17c.), from Old French plat "flat" (see plateau (n.)); formed on analogy of latitude, etc. Meaning "a flat, dull, or commonplace remark" is recorded from 1815. Related: Platitudinous. Hence platitudinarian (n.), 1855; platitudinize (1867).