"Czwartek nie był spokojnym dniem."

Translation: Thursday was not a peaceful day.

[flootzavut]

Appropriate to Christmas Eve 8-o busy busy busy

[EwaPink]

Can you say spokojny dzień instead at the end?

[Jellei]

Maybe as "Czwartek to nie był spokojny dzień", but that sounds a bit if you protested at someone who claimed that it was a peaceful day.

[akikotsukamoto]

I think it is OK to say "the" Thursday

[Jellei]

A comment from one of our British contributors:

It's not wrong but it's very context dependent: it would mean 'The Thursday of the [week/event] were are already talking about' and it probably needs to come in a list of days:
That week was difficult. [The/] Thursday was not a peaceful day and [the/] Friday was worse.
I wouldn't accept it, as no context is given.