Word Origin & History
diaperearly 14c., from O.Fr. diapre "ornamental cloth," from M.L. diasprum, from Medieval Gk. diaspros, from dia- "entirely, very" + aspros "white." Aspros originally meant "rough," and was applied to the raised parts of coins (among other things), and thus was used in Byzantine Gk. to mean "silver coin,"
from which the bright, shiny qualities made it an adj. for "whiteness." Modern sense of "underpants for babies" is continuous since 1837, but such usage has been traced back to 1590s.