regarding Shakespeare's King Richard III, ed. by Richard Grant White (1883)

"To do this piece of ruthful butchery" : —Thus the folio. The quarto of 1597 has, "To do this ruthlesse peece of butchery ; " tlie later quartos, "To do this ruthfull peece," &c. The folio, it will be seen, gives a revised version of the line, the position of the adjective having been changed. Therefore, as the form 'ruthful' was retained on the revision, it should not be changed to 'ruthless,' as it has generally been in modern editions. 'Ruthful' is elsewhere thus used by Shakespeare, and also by other authors of his time, and later : and we now say, with the same force, either a shameful deed or a shameless deed; in one instance meaning that the act causes shame in the observer—in the other, that it shows a lack of shame in the performer. So the same act may be characterized as pitiful, sorrowful, ruthful, or pitiless, sorrowless, ruthless.