that'll be the dayidiom
Definition of that'll be the day
—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!"
Love words? Need even more definitions?Merriam-Webster unabridged
Words at Play
- On Contractions of Multiple Words
- A Look at Uncommon Onomatopoeia
- Is Singular 'They' a Better Choice?