What’s the deal with the word DEAL?
It is found in business and trade. It is currently trending in politics. It is also frequently used in colloquial English.
So here’s the deal:
The noun 
A deal is
1. an agreement, a pact
Some typical verbs phrases are
- reach / come to a deal – After many hours of negotiating we finally managed to reach a deal.
- make / do a deal – I thought we’d made a deal to share the work, but I’m actually doing it all!
A dealbreaker is a factor or issue that can cause an agreement or a relationship to fail. – We really loved the house, but the dealbreaker for us was that it had no garden, so we didn’t buy it.
> When an agreement has – or has not – been reached, we can say:
Deal! / It’s a deal! / We’ve got a deal. // No deal.
2. a considerable amount
a good / great deal (of) 
Stonehenge dates back to 3100 BC and is therefore a good deal older than the pyramids.
I put a great deal of work into this project.
3. a bargain
a good deal
30% off? That’s a very good deal!
I got a really good deal on my car.
I don’t think any other vendor will give you a better deal.
I’m checking the web to see where I can get the best deal.
4. unfair treatment or an unfortunate outcome
a bad / rough / raw deal
Either way, both the UK and the EU will likely get a bad deal from the Brexit.
Trending word in politics
Currently, deal is a hot word in the news as the United Kingdom is negotiating the conditions for its exit from the European Union (referred to as Brexit: Britain + exit = Brexit).
There are basically two options: a soft Brexit, in which both sides come to an agreement, or a hard, or no-deal, Brexit.
The verb
The verb deal is irregular: deal, dealt, dealt.
It has essentially these meanings: 
1. deal (+ in): buy and sell
He deals in antiques.
He was arrested for dealing drugs.
Someone that buys and sells certain goods is called a dealer:
He’s an antiques dealer / car dealer / drug dealer.
2. deal + with: manage, handle; take action about somebody or something; do business
My department deals with customer complaints.
He’s good at dealing with rude people.
She doesn’t deal well with stress.
Our company mainly deals with Asian firms.
3. deal + with: to be about a certain topic
Her latest book deals with the American Civil War.
This poignant film deals with dementia.
4. deal a blow to: to affect plans or hopes
The Brexit could deal a blow to thousands of British citizens living in the EU.
Some colloquial uses of deal
• Deal with it! = Stop complaining and make the best of it.
What’s the deal? Here’s the deal.
• What’s the deal? (informal) = What’s going on here?
What’s the deal with your job? Are you going to get promoted or not?
• Here’s the deal = Let me explain.
So here’s the deal: I’ll stay at their house until Sunday to help them paint the kitchen.
big + deal
• a big deal = something important, difficult or special
Getting married is a big deal for most people.
• no big deal – unimportant, of little consequence 
• make a big deal out of something = exaggerate
It was just a minor cut, but he made a big deal out of it.
• What’s the big deal? = Why are you so excited / upset about it?
• Big deal! (ironic): It’s not as special / important as you say.
– I scored a goal yesterday.
– Big deal – I scored three!