shake on (something)

To grasp someone's hand as a sign that both parties agree to or on something, such as a deal or arrangement. I'd like my lawyers to look over the details of the contract before we shake on it. After several months of negotiations, I think we're now ready to shake on the deal.

shake on it

To confirm an agreement with someone by shaking hands. I can't believe he broke his promise to me after we shook on it and everything! I agree to the terms of this deal, so let's shake on it.

shake (hands) on it/on something

shake hands with somebody to show that you have made an agreement, a deal, etc: ‘OK, I’ll let the car go for $5 000.’ ‘Do you want to shake on it?’ ♢ Let’s shake on it.