Superlative form of chaste: most chaste.(adjective)
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Use "chastest" in a sentence
"Ye know that ye are sprung of the same stock as your sister, best of women, chastest too; hail then for the true nobility of Helen's soul, a quality too seldom found amongst her sex!"
"And so it happened formerly, in the city of Antwerp, that a married woman, who was not the chastest person in the world, was desired by a good fellow to do–you know what."
"He is the chastest prince for women that ever was, for he would often swear that he never kissed any other woman than his own queen."