The moon; a surname of Artemis or Diana. The Roman Diana, who represented the moon, was called Cynthia from Mount Cynthus, where she was born.
And from embattled clouds emerging slow, Cynthia came riding on her silver car.
Cynthia. Pope, speaking of the inconstant character of woman, “matter too soft a lasting mark to bear,” says -
Come, then, the colours and the ground prepare! Dip in the rainbow, trick her off in air; Choose a firm cloud, before it fall, and in it Catch, ere she change, the Cynthia of the minute.
Epistle ii. 17-20.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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