The term is greek in origin and referred to burn offering "holókaustos" - "completely/wholely burned", it was used in this way throughout the middle ages for fire-progroms against Jews (*) and later (1515) to decry the witch-burnings as "the new fire sacrifices" ("nova holocausta").

* "Eodem coronationis die, circa illam sollemnitatis horam qua Filius immolabatur Patri, incceptum est in civitate Londoniae immolare Judaeos patri suo diabolo ; tantaque fuit hujus Celebris mora mysterii, ut vix altera die compleri potuerit holocaustum" - "On the same day of the coronation, about that solemn hour when the Son was sacrificed to the Father, it was begun in the city of London to sacrifice the Jews to their father the devil; and so great was the delay of this famous mystery, that the next day the holocaust could scarcely have been completed" source

Edit: This is btw. describing the events of the coronation of Richard the Lionheart 1189 CE.