dayone
nounUK /ˈdeɪ wʌn/
US /ˈdeɪ wʌn/
The very first day of something new.
From day one, she loved her new school.
RELATED WORDS
OTHER MEANINGS
2. A person who has been involved since the very beginning.
He's a day-one fan of the band.
3. The first day of a project or trip.
On day one of our trip, we visited the beach.
4. The earliest stage of a process.
The team faced problems right from day one.