Many centuries ago in Old England the name shrew (Old English screawa) was applied to a common small animal about the size and appearance of a mouse, though having a long sharp snout.
The source of the name is unknown.
The animals, living chiefly in the woods and feeding upon insects, grubs, and the like, were not destructive, and for some peculiar reason the name by which they were once known dropped into disuse for five or six hundred years.
But the little animals had one characteristic and were thought to possess another which seem to have caused their name to be used in another manner. They were found to be exceedingly pugnacious.
Two would fight over a morsel of food until one was killed; the fallen would then be eaten by the victor. They were also thought to be venomous, and, in popular superstition, if one were to run over the leg or body of a farm animal, that animal was then believed to be poisoned.
It might be cured if a live shrew were imprisoned in a hole bored into an ash tree, and then twigs of that ash gently brushed over the affected parts of the animal.
Because of the pugnacity and suspected venomosity, the term shrew was transferred to either a man or woman whose character was evil or malignant, especially to one, usually a woman (now always a woman), whose disposition was to nag, scold, or rail.
This led to the formation of the verb to shrew.
Its past participle was shrewd, and this, in its early sense, meant evil-disposed, vicious, dangerous, but has passed into sharp or acute, or into astute or keen-witted.