day one

noun

variants often Day One
Synonyms of day onenext
: the first day or very beginning of something

Examples of day one in a Sentence

We've known this about the project since Day One. since day one of this project, we've always insisted that we would create the best product possible without any consideration of cost
Recent Examples on the Web
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Trump campaigned last year on reducing the cost of living on day one of his presidency. Joey Garrison, USA Today, 16 Dec. 2025 Build with that trajectory in mind —design for scale, interoperability, and governance from day one. Charles Lamanna, Fortune, 15 Dec. 2025 And that was within the first hour of day one. Victoria Uwumarogie, Essence, 9 Dec. 2025 Laros confirmed that on day one, Spectra successfully ran the HPCG benchmark, molecular dynamics code LAMMPS, and SPARTA, a Monte Carlo simulation tool widely used at Sandia. Neetika Walter, Interesting Engineering, 8 Dec. 2025 See All Example Sentences for day one

Word History

First Known Use

1953, in the meaning defined above

Time Traveler
The first known use of day one was in 1953

Browse Nearby Words

Cite this Entry

“Day one.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/day%20one. Accessed 20 Dec. 2025.

Last Updated: - Updated example sentences
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