From the Greek meta “about”.
According to Northrop Frye (Fables of Identity: Studies in PoeticMythology (New York: Harcourt Brace and World, 1963), metahistory is a synonym for the philosophy of history, or, at a less exalted but no less powerful level, of a system of anthropological or philosophical principles which underpin the knowledge of any historical account and are tacitly or explicitly believed by the historian to run throughout human experience, making it possible to ground an historical account in principles which are themselves not subject to the one great law of history – that everything is mutable. A famous example of a metahistorical position is found in Marx's dictum “all history is the history …
Clark, Robert. "Metahistory". The Literary Encyclopedia. First published 08 November 2007
[https://www.litencyc.com/php/stopics.php?rec=true&UID=716, accessed 23 February 2019.]