"an author of history," mid-15c., as if from Medieval Latin *historianus, from Latin historia "narrative of past events; narrative account, report" (see history). Compare Old French ystorïen (adj.). As "writer of history in the higher sense" (distinguished from an annalist or chronicler), from 1530s. An Old English word was þeod-wita, also wyrd-writere "one who writes an account of events, a historian or historiographer" (see weird). The classical Latin word was historicus (adj.) used as a noun. Holinshed has historician.
[T]he historian's fallacy is the error of assuming that a man who has a given historical experience knows it, when he has had it, to be all that a historian would know it to be, with the advantage of historical perspective. [David Hackett Fischer, "Historians' Fallacies," 1970]