not performing, or ready to perform, the duties required by one who has the right to claim submission, obedience, or deference; submissive to natural or legal superiors; disobedient, as to parents or superiors;
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Uses:
If both had owned plantations in Louisiana, they would have been as like as two old bullets cast in the same mould."
"What an undutiful boy you are!" said Miss Ophelia.
"I don't mean them any disrespect," said St. Clare. "You know reverence is not my forte.[...]"
Harriet Beecher Stowe. Uncle Tom's Cabin
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As the son grew a young man, he turned out riotous, extravagant, undutiful,—altogether bad.