Where does “substantive genitive” come from?

substantive genitive (English) comes from English substantive, from Middle English substantif, from Old French substantif.

Ancestry of “substantive genitive”, step by step

substantive genitive traces back through two separate lines of ancestry.

via English substantive

StepLanguageWordMeaning
1Englishsubstantiveof the essence or essential element of a thing;...
2Middle Englishsubstantif
3Old Frenchsubstantif

via English genitive

StepLanguageWordMeaning
1EnglishgenitiveOf or pertaining to that case which expresses a...
Every word from Old French substantifEvery word from Middle English substantifEvery word from English substantive