The Great Bombay Name Change
In the mid-1990s, Shiv Sena, the Hindu nationalist party in power in Bombay, decided to change the city’s name to Mumbai, a name often used in local languages that derives from Mumba Devi, the patron Hindu goddess of the island's original residents, the Koli fishermen. Many residents still call their city Bombay, however. The renaming of the city was simply the grandest example of an epidemic that has swept the former Bombay in the last 20 or so years—Crawford Market became Mahatma Jyotiba Phule Market, Victoria Terminus became Chhatrapati Shivaji Terminus, Marine Drive became Netaji Subhash Chandra Bose Marg. And those are just the big ones; indeed, nearly every road and lane in Mumbai has more than one name. Not only that, but each intersection often has its own name, too, and each individual corner might also have its own moniker (they're often named by local government officials or rich locals for members of their families).
The fact is, though, that as a tourist—and even as a local—you don't need to know any of the new names: No one calls Marine Drive anything but Marine Drive, and no one calls the Causeway anything but the Causeway. Although you will get the odd "CST" for Victoria Terminus, no one uses the new full name, so don't worry about pronouncing it: VT will do just fine.