Alkahest (a pseudo-Arabic word believed to have been invented by Paracelsus) is a liquid, much sought after by the alchemists, having the power of dissolving gold and every other substance, which it was supposed would possess invaluable medicinal qualities.

Such a substance is as of 1935 impossible to obtain, the closest is likely aqua regia

• Text from the public domain 1911 Encyclopaedia Britannica.