It was Jayasamhita (pronounced: jaya-samhitah). Name has its root in the fact that its climax is winning of Pandavas over Kauravas. Victory is called jaya in Sanskrit. Also there is a special cryptic way to represent numbers, in Sanskrit, and in that code, jaya means 18, which is number of books (parvas) in Mahabharata. Hence this name. Its another name is also Shatasaahasri samhitaa (literally, collection of a hundred thousand verses).
The original name of the Mahabharata is Mahabharata.
Devrata or gangaputra
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jayasanhita
Jaya
Mahabharata itself. It is an epic narrative of the Kurukshetra War and the fates of the Kauravas and the Pandavas.
Dritharashtra
dhussala
Delhi
Arjun
Jaya
"Indraprastha" according to the Mahabharata