E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A small insectivorous mammal, resembling a mouse in form. It was supposed to have the power of injuring cattle by running over them; and to provide a remedy our forefathers used to plug the creature into a hole made in an ash-tree, any branch of which would cure the mischief done by the mouse. (Anglo-Saxon, screawa, a shrew-mouse; mouse is expletive.)