Meanings
- New ZealandidiomaticinformalSaid in reply to something that one believes will never happen.
I’m going to get into work on time today. — That’ll be the day!
1 more example
Transmission from Klingon ship: Federation ship Enterprise. Surrender and prepare to be boarded. / Jean-Luc Picard (Patrick Stewart): That will be the day.
1990, Trent Christopher Ganino, Eric A. Stillwell, “Yesterday's Enterprise”, in Star Trek: The Next Generation, season 3, episode 15, spoken by Jean-Luc Picard (Patrick Stewart)Synonyms: that'll be the frosty Friday
Synonyms & antonyms
phraseSaid in reply to something that one believes will never happen.
Origin
Originally referring to a significant day in the future regarded as worth waiting for.
Full word history & related roots →Translations
Finnish sen päivän kun näkisi
- sen päivän kun näkisisaid in reply to something that one believes will never happen
French quand les poules auront des dents, c’est pas demain la veille
- quand les poules auront des dentssaid in reply to something that one believes will never happen
- c’est pas demain la veillesaid in reply to something that one believes will never happen
Greek ζήσε Μάη μου
- ζήσε Μάη μου (zíse Mái mou)said in reply to something that one believes will never happen
Polish akurat
- akuratsaid in reply to something that one believes will never happen
Spanish el día que la vaca vuele
- el día que la vaca vuelesaid in reply to something that one believes will never happen
Cite this entry
that'll be the day. (n.d.). In WatkinsX Dictionary. Retrieved November 5, 2026, from https://dictionary.watkinsx.com/word/that'll%20be%20the%20day
“that'll be the day.” WatkinsX Dictionary, https://dictionary.watkinsx.com/word/that'll%20be%20the%20day. Accessed November 5, 2026.
WatkinsX Dictionary, s.v. “that'll be the day,” accessed November 5, 2026, https://dictionary.watkinsx.com/word/that'll%20be%20the%20day.
Source: that'll be the day on Wiktionary, CC BY-SA 4.0.