This rare adjective describes something associated with donkeys. In both New Testament occurrences, it qualifies a millstone—specifically the large, heavy type that would be turned by a donkey walking in circles (as opposed to smaller hand mills). Jesus uses this vivid image when warning against causing children to stumble: such a person would be better off with a donkey-driven millstone hung around their neck and drowned in the sea. The phrase captures the industrial scale of the judgment.