Related Clues:
- Gets grayer, usually
- A billion years, to geologists
- "Fun for children of all ___!"
- Many generations
- Mellows or yellows
- A long stretch
- Umpteen millennia
- Mind-boggling time span
- Reeeeeeally long time
- Longest division of geologicalà time
- Gigayear
- Forever and a day, facetiously
- It's a real stretch
- Astronomically long time
- It seemingly never ends