Define noir: crime fiction featuring hard-boiled cynical characters and bleak sleazy settings — noir in a sentence. The Urban Dictionary Mug. One side has the word, one side has the definition. Microwave and dishwasher safe. Lotsa space for your liquids. Buy the mug. 2. Noir definition, black; noting the black numbers in roulette. See more. Pinot Noir · Beurre noir · Boudin noir.