fissile

Merriam-Webster's Word of the Day for February 8, 2024 is: fissile \FISS-ul\ adjective

Fissile describes materials that are capable of undergoing [fission](https://www.merriam-webster.com/dictionary/fission)—that is, the process in which the nucleus of a heavy atom is split apart, releasing a large amount of energy. Fissile can also be used to describe something, such as wood or crystals, capable of or prone to being split or divided in the direction of the grain along natural planes.

// The wood of most [conifer](https://www.merriam-webster.com/dictionary/conifer) species is fissile, making it much easier to cut than that of sycamore and [hornbeam](https://www.merriam-webster.com/dictionary/hornbeam).

[See the entry >](https://www.merriam-webster.com/dictionary/fissile)

Examples:

"In Oak Ridge, Tennessee, a whopping 50,000 people worked to create the material, enriched uranium, needed for Los Alamos' bomb, while thousands more created another fissile material, plutonium, in Hanford, Washington. Including the hundreds of thousands of construction workers who built these labs and boomtowns, 'the Oak Ridge and Hanford sites alone hired more than a half-million employees,' the U.S. Department of Energy said." — Mark Kaufman, Mashable.com, 2 Sept. 2023

Did you know?

When scientists first used fissile back in the 1600s, the notion of splitting an atom would have seemed far-fetched indeed. At that time, people thought that atoms were the smallest particles of matter that existed and therefore could not be split. Fissile (which can be traced back to the Latin verb findere, meaning "to split") was used in reference to things like rocks. When we hear about fissile materials today, the reference is usually to nuclear fission: the splitting of an atomic nucleus that releases a huge amount of energy. But there is still a place in our language for the original sense of fissile (and for the noun fissility, meaning "the quality of being fissile"). A geologist or builder, for example, might describe [slate](https://www.britannica.com/science/slate-geology) as being fissile, as it splits readily into thin slabs.