Where does “femtogramme” come from?

femtogramme (English) comes from English gramme — gram.

Ancestry of “femtogramme”, step by step

femtogramme traces back through two separate lines of ancestry.

via English gramme

StepLanguageWordMeaning
1Englishgrammegram

via English femto

StepLanguageWordMeaning
1Englishfemto
Every word from English gramme
femtogramme — Etymology, Origin & Word History | Etymology Explorer