day one

noun

variants often Day One

: the first day or very beginning of something

Synonyms of day one

• beginning
• start
• inception
• commencement
• alpha
• onset
• launch

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

His line-up will look different on day one of the World Cup (that goes without saying), but the roster has started to ooze tangible depth. —Phil Hay, New York Times, 19 Nov. 2025

Advertisement In New Jersey, Governor-Elect Mikie Sherrill has championed efforts to reduce utility costs for working families, pledging on day one to declare a formal State of Emergency on Utility Costs freezing rates for families across the state. —Alanna McCargo, Time, 17 Nov. 2025

This means this new version is still more expensive than if customers bought the console on day one. —PC Magazine, 12 Nov. 2025

Be thoughtful about bringing in talent that’s trained to get even the most complex AI projects done well and delivering value from day one. —Kathleen Walch, Fortune, 11 Nov. 2025

Word History

First Known Use

1953, in the meaning defined above

Rhymes for day one

• begun
• grandson
• gudrun
• handgun
• homespun
• outdone
• outrun
• pashtun
• redone
• rerun
• shotgun
• someone