ˌbig ˈdeal noun [singular] spoken

1. used to say that you do not think something is as important as someone else thinks it is:
It’s just a game. If you lose, big deal.
What’s the big deal? It’s only a birthday, not the end of the world.
It’s no big deal. Everybody forgets things sometimes.

2. an important or exciting event or situation:
This audition is a big deal for Joey.

3. make a big deal of/out of/about something to get too excited or upset about something, or make something seem more important than it is:
I know I’m probably making a big deal out of nothing, but I’m worried about you.

[TahlilGaran] Dictionary of Contemporary English ▲

big deal
a subject, situation, or event which people think is important.
I don't know why this issue has become such a big deal.

Losing the match was no big deal.

All I said was, I'm going to have a baby - what's the big deal?

Yes, it's his birthday today, but he doesn't want to make a big deal of it.
(= make people notice it by having a special celebration)
something important or special.
They made a big deal about inviting the president to the reception.

Usage notes: often used to say that something represented as important is in fact only ordinary:
"I ran five miles this morning." "Big deal! I ran ten."

They called him a hero, but he said it was no big deal.

[TahlilGaran] English Idioms Dictionary ▲

Big deal!
[informal]
something that you say to show that you do not think that something is either important or interesting.
'Did I tell you Ann got a new car?' 'Big deal!'

[TahlilGaran] English Idioms Dictionary ▲

big deal
interj., slang, informal (loud stress on the word "deal") Trifles; an unimportant, unimpressive thing or matter.
So you became college president
■ big deal!

[TahlilGaran] English Idioms Dictionary ▲