One billion years, officially (3)

I believe the answer is:

eon

(Other definitions for eon that I've seen before include "Prolonged period" , "Era" , "Geological period" , "billion years" , "plenty of time" .)

I've seen this clue in the Universal.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.