Gulielmian

adjective2

1. •
   (rare) Of or relating to a person named William, chiefly a ruler.
2. •
   (rare) Of, from, or characteristic of the reign of King William IV (1830–1837) or a future King William V of the United Kingdom (currently William, Prince of Wales).

   • Such were my early but forgotten productions,—still-born innocents. The writers of the Gulielmian age, of whom so much had been asked, did, of course, just nothing at all for them. — 1872