forum
Meaning: a medium for lecture or discussion
Usage: Some radio talk-shows provide a good forum for political debate.
interlocutor
Meaning: someone who participates in a dialogue or conversation
Usage: When the officials could not come to an agreement over the correct cover of the flags, the prime minister acted as an interlocutor.
inquisitor
Meaning: one who inquires, especially in a hostile manner
Usage: The inquisitor was instructed to knock on every door in town in order to find the fugitive.
colloquy
Meaning: a formal conversation or dialogue
Usage: The two scholars held a colloquy about the meaning of the old poem.
interrogate
Meaning: to question thoroughly
Usage: The detective had to interrogate each witness before drawing a conclusion.
query
Meaning: to ask; to question
Usage: The editor decided to query the source before publishing the claim.