"noting the time of an action occurring prior to another specified time," c. 1500, pluperfyth, shortened from Latin (tempus praeteritum) plus (quam) perfectum "(past tense) more (than) perfect." This translates Greek khronos hypersyntelikos. See plus and perfect (adj.). In grammar, denoting the pluperfect tense of a verb, as Latin amaveram, English "I had loved."
Qwerby knowyst þe pretyr tens pluperfyth? ffor it spekyth of tyme more þan perfythly passyd, & hath þis Englysch wurd 'hadde', as 'amaueram, I had louyd'. [English grammatical text, c. 1500]