E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Hewing blocks with a razor. Livy relates how Tarquinius Priscus, defying the power of Attus Navus, the augur, said to him, Tell me, if you are so wise, whether I can do what I am now thinking about. Yes, said Navius. Ha! ha! cried the king; I was thinking whether I could cut in twain that whetstone with a razor. Cut boldly! answered the augur, and the king cleft it in twain at one blow.