Where does “マックス” come from?

マックス (Japanese) comes from English Max, from English maximum, from Latin Maximus, from Proto-Italic *magisVmos.

Ancestry of “マックス”, step by step

StepLanguageWordMeaning
1EnglishMax—
2EnglishmaximumThe highest limit; The greatest value of a set or...
3LatinMaximusthe greatest
4Proto-Italic*magisVmos—
Every word from Proto-Italic *magisVmos →Every word from Latin Maximus →Every word from English maximum →