Definition of "underpayment" []

• An insufficient payment (noun)
• The act of making such a payment (noun)
• The amount by which a payment is insufficient (noun)

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• "On Tuesday, when Mr. Geithner's failures were first reported by The Wall Street Journal, the Obama transition office issued a statement calling his underpayment of taxes "honest mistakes.""
• "A potential underpayment by the Perry campaign to Mr. Pardo for use of his plane was reported Tuesday by the New York Times."
• "If the amount under the AMT is higher than what they would otherwise owe, they must pay the higher amount, or risk incurring underpayment penalties."