fossilize

verb4

1. •
   To make into a fossil.
2. •
   To become a fossil.
3. •
   (figurative) To become inflexible or outmoded.

   • I was getting fossilised myself, but of late my stock of ideas has been very much enlarged. — 1886
4. •
   (figurative) To make antiquated, rigid, or fixed; to deaden.

   • Ten layers of birthdays on a woman's head / Are apt to fossilize her girlish mirth. — 1856