A picture is worth 1,000 words here... and context for the item in question (such as what the circuit does, where it resides int he circuit, etc.) would also be useful.
From the size, value, and voltage, it sounds like a rectangular film capacitor. I do believe some are made with two leads at each end for vibration purposes. If it is potted on the bottom where the leads are, then it probably is a rectangular film.