The Collaborative International Dictionary of English v.0.48:

Hercynian \Her*cyn"i*an\, a. [L. Hercynia silva, Hercynius
   saltus, the Hercynian forest; cf. Gr. ? ?.]
   Of or pertaining to an extensive forest in Germany, of which
   there are still portions in Swabia and the Hartz mountains.
   [1913 Webster]