c. 1600, "subject for investigation," also "systematic search," from Latin disquisitionem (nominative disquisitio) "an inquiry, investigation," noun of action from past participle stem of disquirere "inquire," from dis- "apart" (see dis-) + quaerere "seek, ask" (see query (v.)). Sense of "long speech" first recorded 1640s.[disquisition etymology, disquisition origin, 英语词源]