1. A makeshift bomb, usually consisting of a gasoline-filled bottle and a wick, that is ignited before it is thrown at a target. The riot police moved in after the demonstrators started throwing Molotov cocktails.

2. By extension, something that has an explosive or otherwise negative impact on a person or situation. If you say anything negative about school board, it will be a real Molotov cocktail at this dinner party, believe me! His arrest was the Molotov cocktail that brought the whole scandal to light.