day one noun
or Day One
or Day One
Learner's definition of DAY ONE
[singular]
: the first day or very beginning of something第一天 -
We've known this about the project since/from Day One.從項目開始的第一天起我們就了解這個情況。
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The new governor will start implementing these changes on day one. [=the first day of the governor's term]新州長將在他上任的第一天開始實施這些變更。