The phrase "a very significant day" is correct and usable in written English.
You can use it to emphasize the importance of a particular day in a specific context, such as an event or milestone.
Example: "Today is a very significant day in our history as we celebrate the anniversary of our independence."
Alternatives: "an extremely important day" or "a highly notable day".
And we are conducting this interview on, you know, a very significant day.
A woman named Roberta told me, "I'm here because it's Good Friday and it's a very significant day that we remember in the Christian calendar.
A woman called Roberta told me, "I'm here because it's Good Friday and it's a very significant day that we remember in the Christian calendar.
Monday, August 22, 2016 will be a very significant day for me as my youngest daughter, Sophie, starts full-time work for the first time in her life.
"It's a very important day, a very significant day.
Speaking at a Yes Scotland event on the Royal Mile in Edinburgh, the first minister said: "I think it is a very significant day in the referendum campaign.
Sunday, 22 July 2012, could be a very significant date for Yorkshire's bid and British cycling.
"This is a very significant deal for this organization," Reds General Manager Walt Jocketty said Monday at a news conference in Cincinnati.
They'll certainly be seen by everybody inside the stadium, and a very significant reminder of that day," he said.
Third, off-farm income is a very significant component of present-day Maasai livelihoods, usually more so than agriculture, but ranges from poorly paid, insecure, often dangerous work (miners, watchmen, sex workers) to secure jobs with wider political/economic prospects (teachers, MPs).
Based on the results presented herein, the G2 (rCP40), G4 (rCP40 + CP09) and G5 (prime-boost) groups had a very significant induction of IgG1, mainly from day 30 after the start of the trail.
