day one

noun, often capitalized D&O
Updated on: 8 Nov 2017

Definition of day one

: the first day or very beginning of something

Examples of day one in a Sentence

  1. We've known this about the project since Day One.

  2. 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 of day one from the Web

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'day one.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of day one

1971


DAY ONE Defined for English Language Learners

day one

noun

Definition of day one for English Language Learners

  • : the first day or very beginning of something


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