Source : Webster's Revised Unabridged Dictionary (1913)

Thionaphthene \Thi`o*naph"thene\, n. [Thiophene + naphthalene.]
   (Chem.)
   A double benzene and thiophene nucleus, {C8H6S}, analogous to
   naphthalene, and like it the base of a large series of
   derivatives. [Written also {thionaphtene}.]