1812, "dullness, insipidity of thought, triteness," 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, trite, or commonplace remark," especially a truism uttered as if it were a novelty, is recorded from 1815. Related: Platitudinous (1862). Hence platitudinarian (n.) "one who indulges in platitudes," 1855; platitudinize (1867).
A commonplace is a thing that, whether true or false, is so regularly said on certain occasions that the repeater of it can expect no credit for originality ; but the commonplace may be useful.
A platitude is a thing the stating of which as though it were enlightening or needing to be stated convicts the speaker of dullness ; a platitude is never valuable. [Fowler]