Rashi on Deuteronomy 20:20/רש"י על דברים כ׳:כ׳

1עד רדתה [AND THOU SHALT BUILD BULWARKS AGAINST THE CITY …] UNTIL רדתה — This (the word רדתה) means “subduing”, [and the meaning is, thou shalt besiege it until] it becomes submissive.