the foggiest notion

A basic, vague, or rudimentary knowledge or understanding (about something). Often used in negative constructions. A: "Do you know where the car keys are?" B: "I haven't the foggiest notion. Sorry." Do you have the foggiest notion how much this mistake is going to cost the company? Even though I could speak a little Japanese, I could only pretend to have the foggiest notion what the woman was talking about.