Where does “mega-storm” come from?

mega-storm (English) comes from English storm, from Middle English storm, from Old English storm, from Proto-West Germanic *sturm, from Proto-Germanic sturmaz, from Proto-Indo-European (s)twer- — to rotate, swirl, twirl, move around; to turn...

Ancestry of “mega-storm”, step by step

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

via English storm

StepLanguageWordMeaning
1EnglishstormAny disturbed state of the atmosphere, especially...
2Middle EnglishstormA storm; an instance of intense wind and...
3Old Englishstormstorm
4Proto-West Germanic*sturmstorm
5Proto-Germanicsturmazstorm
6Proto-Indo-European(s)twer-to rotate, swirl, twirl, move around; to turn...

via English mega

StepLanguageWordMeaning
1EnglishmegaVery large; great; excellent
2Ancient Greekμέγαςbig, large; great, mighty, loud; marvelous,...
3Proto-Indo-Europeanmeǵh₂sgreat
Every word from Proto-Indo-European (s)twer-Every word from Proto-Germanic sturmazEvery word from Proto-West Germanic *sturm