fallout

American  

[fawl-out] / ˈfɔlˌaʊt /

Or fall-out

noun

1. the settling to the ground of airborne particles ejected into the atmosphere from the earth by explosions, eruptions, forest fires, etc., especially such settling from nuclear explosions radioactive fallout.

2. the particles themselves.

3. an unexpected or incidental effect, outcome, or product.

   the psychological fallout of being obese.

4. effects; results.

   emotional fallout from a divorce.

---

fallout British  

/ ˈfɔːlˌaʊt /

noun

1. the descent of solid material in the atmosphere onto the earth, esp of radioactive material following a nuclear explosion

2. any solid particles that so descend

3. informal side-effects; secondary consequences

---

verb

1. informal to quarrel or disagree

2. (intr) to happen or occur

3. military to leave a parade or disciplinary formation

1. military the order to leave a parade or disciplinary formation

Etymology

Origin of fallout

First recorded in 1945–50; noun use of verb phrase fall out

Explanation

Fallout is the cloud of radioactive material that falls from the sky after a nuclear blast. Fear of the effects of fallout is just one reason some people are nervous about nuclear energy. Nuclear fallout settles on the ground and in the atmosphere after a nuclear bomb explodes or a reaction occurs at a damaged nuclear power plant. The dangers of this kind of fallout are enormous, including immediate death and long-term illness caused by breathing and eating the radioactive dust. Another kind of fallout is more figurative — it's any kind of negative effect or result, like the fallout from telling your family you're getting an enormous tattoo.

Example Sentences

This week, the fallout from Lord Mandelson's sacking as the UK's ambassador to the US continued, Prince Louis celebrated his eighth birthday and the stars of The Devil Wears Prada 2 hit the red carpet.

From BBC • Apr. 23, 2026

The U.S. stock market has been relatively sanguine about the fallout from these shortages, but economists caution it could take a bit of time until the full ramifications are seen in the economy.

From Barron's • Apr. 23, 2026

For investors, it’s an early sign that the economic fallout from the Iran conflict may be far from over, even as markets appear to be looking past it.

From MarketWatch • Apr. 21, 2026

Maine lawmakers on Tuesday passed a ban on large data-center construction, making it the first state to enact such a measure as communities around the U.S. deal with fallout from the artificial-intelligence boom.

From The Wall Street Journal • Apr. 15, 2026

The concept appealed to both Teller and Lawrence, who understood that public alarm about fallout could threaten the lab’s existence.

From "Big Science" by Michael Hiltzik