To deliver less, or at an inferior level, than promised or expected(verb)
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Use "underdeliver" in a sentence
"Unfortunately, the Democrats who run Washington believe in this time of fiscal challenges we should continue propping up government programs that overspend and underdeliver."
"This sounds straightforward, but it typically requires conscious attention and courage from the CEO; otherwise, the top team can underdeliver for an extended period of time."
"Some members expressed a fear that again euro-zone governments would "overpromise and underdeliver" in the face of the crisis."