1546, from M.Fr.
sincérité (1519), from L.
sinceritatem (nom.
sinceritas), from
sincerus "sound, pure, whole," perhaps originally "of one growth" (i.e. "not hybrid, unmixed"), from
sem-, sin- "one" + root of
crescere "to grow" (see
crescent). Ground sense is of "that which is not falsified."