noun, feminine/syp.stɑ̃.ti.va.sjɔ̃/plural: substantivations
substantivation is feminine in French.
substantivization, nominalization
“La substantivation, très vivante en ancien français, ne se produit plus guère aujourd’hui que dans le discours philosophique.” — Nominalization, very active in Old French, hardly ever occurs today except in philosophical discourse.
From substantiver + -ation.