Where does “mega-annum” come from?

mega-annum (English) comes from English mega, from Ancient Greek μέγας, from Proto-Indo-European meǵh₂s — great.

mega-annum (English): a period of 1 million years

Definitions

  1. a period of 1 million years

Ancestry of “mega-annum”, step by step

mega-annum traces back through two separate lines of ancestry.

via English mega

StepLanguageWordMeaning
1EnglishmegaVery large; great; excellent
2Ancient Greekμέγαςbig, large; great, mighty, loud; marvelous,...
3Proto-Indo-Europeanmeǵh₂sgreat

via Latin annum

StepLanguageWordMeaning
1Latinannumaccusative singular of annus; year
Every word from Proto-Indo-European meǵh₂sEvery word from Ancient Greek μέγαςEvery word from English mega
mega-annum — Etymology, Origin & Word History | Etymology Explorer