Source : Webster's Revised Unabridged Dictionary (1913)

Heterochronism \Het`er*och"ro*nism\, Heterochrony
\Het`er*och"ro*ny\, n. [Gr. ? of different times; ? other + ?
   time.] (Biol.)
   In evolution, a deviation from the typical sequence in the
   formation of organs or parts.