The lady-love of Abrocomas in Xenophon's romance, called Ephesiaca. Shakespeare has borrowed from this Greek novel the leading incidents of his Romeo and Juliet , especially that of the potion and mock entombment. N.B. This is not the historian, but a Xenophon who lived in the fourth Christian century.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894