that'll be the day
idiom
—used to say that one thinks something will not happen
"Do you think he'll ever admit he made a mistake?" "That'll be the day!"
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Cite this Entry
“That'll be the day.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/that%27ll%20be%20the%20day. Accessed 19 Apr. 2024.
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