Pronunciation: (fôl'out"),[key] —n. 1. the settling to the ground of airborne particles ejected into the atmosphere from the earth by explosions, eruptions, forest fires, etc., esp. such settling from nuclear explosions (radioactive fallout). Cf. rainout. 2. the particles themselves. Cf. rainout. 3. an unexpected or incidental effect, outcome, or product: the psychological fallout of being obese. 4. effects; results: emotional fallout from a divorce.Also,fall'-out".