Hi there. All of them convey different concepts. "Deal" is more of an informal agreement that parties agreed upon. "Pact" is more formal agreement, usually between two or more nations. "Accord" is an official agreement sometimes issued by court as an order and is similar to pact. I wouldn't use any of them apart from "deal" in a given sentence.
Hi Fandorin, Thanks a lor for your explanations! I have no intention to substitute 'deal' for my given options at all. It's just to explain the meaning to the students. I just have to be sure that I'm not writing something which is not logical or very unnatural. The reason to ask it's because the students have a glossary
The words pact and accord may imply additional details that are not part of the definition for deal. It would be safest to revert to the most basic definition of simply being an agreement.