Etymology From Latin benefactus (“benefited”) plus -ive. Attested since the twentieth century.
1
Human sciences, Linguistics, Sciences Of or pertaining to the linguistic form or case or the semantic role of the beneficiary of an action. Expressed in English as "on behalf of", "in behalf of", "on one's behalf", or similar.
Normally, the repeated benefactive suffix is not found after the telic form of the verbal stem1935, Charles Voeglin, Tübatulabal Grammar, University of California Publications in American Archaeology and Ethnology, volume 34, page 111:
Etymology From Latin benefactus (“benefited”) plus -ive. Attested since the twentieth century.
1
Human sciences, Linguistics, Sciences A term or sentence element that serves a benefactive role or that is inflected for the benefactive case or a similar case (such as the dative case).