A colloquy is a formal talk, the opposite of a chat, such as the colloquy you have with your boss about a serious matter — far different from how you'll talk to your friends about it afterward.
To correctly pronounce colloquy, accent the first syllable: "KOLL uh kwee." The word comes from the Latin prefix com-, meaning "together," and loquium, meaning "speaking." That adds up to "speaking together." You probably recognize loqui, meaning "to speak," in words like locution and colloquial, which also involve speaking.