day one

American  

noun

1. (often initial capital letters) the very first day or beginning of something.

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Etymology

Origin of day one

First recorded in 1975–80

Example Sentences

And this past January the General Services Administration updated its Open Source Software Policy to require that new custom code be developed in public repositories from day one.

From The Wall Street Journal • Apr. 17, 2026

A huge component of “NCIS” that has remained consistent from day one is that it’s more than a case-of-the-week procedural.

From Los Angeles Times • Mar. 24, 2026

"We did not want this war. From day one, we have called for de-escalation," Denmark's Foreign Minister Lars Lokke Rasmussen told Danish media in Brussels before an EU foreign ministers' meeting.

From Barron's • Mar. 16, 2026

"It's like going back to day one," she says of their trauma.

From BBC • Mar. 7, 2026

The West Virginia engineer she had met on day one played oboe in a local symphony.

From "Hidden Figures" by Margot Lee Shetterly

Related Words

• birth
• creation
• dawn
• inauguration
• inception
• introduction
• onset
• opening
• outset
• starting point
• top