day one

noun

often capitalized D&O
: 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.
Every system is designed for manufacturability from day one, enabling rapid iteration and high-volume production. Prabhat Ranjan Mishra, Interesting Engineering, 27 Oct. 2025 Betting on the local community From day one, the project engaged local residents—construction crews, staff, and suppliers of food and materials were recruited from nearby villages. Maria Williams, USA Today, 27 Oct. 2025 They should have been gone on day one, which conveniently coincided with their council’s statutory biannual review and renewal, neither of which appears to have been conducted. Paul Du Quenoy, MSNBC Newsweek, 24 Oct. 2025 Advertisement Starting again from day one The world that follows is quieter. Jp Mangalindan, Time, 24 Oct. 2025 See All Example Sentences for day one

Word History

First Known Use

1971, in the meaning defined above

Time Traveler
The first known use of day one was in 1971

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Cite this Entry

“Day one.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/day%20one. Accessed 31 Oct. 2025.

Last Updated: - Updated example sentences
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