E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Stone (1 syl.).
The sacred stone of the Caaba (q.v.) is, according to Arab tradition, the guardian angel of Paradise turned into stone. When first built by Abraham into the wall of the shrine it was clear as crystal, but it has become black from being kissed by sinful man.
A hag-stone. A flint with a natural perforation through it. Sometimes hung on the key of an outside door to ward off the hags. Sometimes such a stone used to be hung round the neck for luck; sometimes on the bedstead to prevent nightmare; and sometimes on a horse-collar to ward off disease.
Leave no stone unturned. Omit no minutiæ if you would succeed. After the defeat of Mardonius at Platæa (B.C. 477), a report was current that the Persian General had left great treasures in his tent. Polycrtes (4 syl.) the Theban sought long but found them not. The Oracle of Delphi, being consulted, told him to leave no stone unturned, and the treasures were discovered.