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