late 14c., "judicial investigation, act or process of inquiring," from Old French inquisicion "inquiry, investigation" (12c., Modern French inquisition), from Latin inquisitionem (nominative inquisitio) "a searching into, a seeking; legal examination, a seeking of grounds for accusation," noun of action from past participle stem of inquirere (see inquire).
In Church history, inquisitors were appointed from 382 C.E. to root out heretics; the ecclesiastical court appointed 13c. by Innocent III to suppress heresy never operated in Britain. The English word began to be used in this sense (and with a capital initial letter) after c. 1500, and usually refers to the office's reorganization 1478-1483 in Spain, where it fell under the control of the state as what is commonly called the Spanish Inquisition, noted especially for its severity, secrecy, and the number of its victims.