AFAIK, Mercury, Quicksilver, and Element should be safe. Even though there are companies that use those names, they're just regular old English word

That has nothing to do with it. Especially considering that Mercury market collaboration and messaging solutions.

Oracle is a plain English word. Good luck in trying to use it to name any computer application ;-) A registered trade mark is a registered trade mark. English word or not.

If you're going to be making a commercial product go find a lawyer. If you're not, doing what Liz suggested and find something that doesn't come up with any google results would seem a sensible option.