E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A horsewoman, a fighting or masculine woman. The word means without breast, or rather, deprived of a pap. According to Grecian story, there was a nation of women in Africa of a very warlike character. There were no men in the nation; and if a boy was born, it was either killed or sent to his father, who lived in some neighbouring state. The girls had their right breasts burnt off, that they might the better draw the bow.
These dreadful Amazons, gallant viragoes who . . carried victorious arms into Syria and Asia Minor.J. E. Chambliss: David Livingstone (Introduction, p. 24).