Donative is not a noun. The CoCA has no occurrence of donative, and the CBE has only one, in which donative is clearly an adjective rather than a noun.
Also, as an elderly native speaker of AmE who also has some experience of BrE, I have never seen or heard the word donative.
These supposed online dictionaries that claim "donative" is a noun are just plain wrong. It would take the OED to convince me otherwise.
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