fis·​sile ˈfi-səl How to pronounce fissile (audio)
: capable of or prone to being split or divided in the direction of the grain or along natural planes of cleavage
fissile wood
fissile crystals
: capable of undergoing fission
fissility noun

Did you know?

When scientists first used fissile back in the 1600s, the notion of splitting the nucleus of an atom would have seemed far-fetched indeed. In those days, 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 Latin findere, meaning "to split" or "to cleave") 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, for example, might refer to slate as being fissile.

Examples of fissile in a Sentence

Recent Examples on the Web One way for North Korea to boost its nuclear stockpile is to ramp up production of lower-yield tactical weapons that require less fissile material. Time, 9 Jan. 2023 The new system retains the latter’s ability to burn the widest possible range of fuels — including not just spent nuclear fuel, but also the ordinarily non-fissile uranium-238. M. Mitchell Waldrop, Discover Magazine, 26 Feb. 2019 The dirty bomb speculation is tied to comments made by Russian Defense Minister Sergei Shoigu, and repeated last week by Putin, suggesting Ukraine planned to detonate a device loaded with fissile material on its own territory. Karoun Demirjian, Washington Post, 2 Nov. 2022 This was eliminated in the final draft which calls for the immediate start of negotiations on a treaty banning production of fissile material. Edith M. Lederer, ajc, 26 Aug. 2022 Most atoms do not fission, but the isotopes of certain elements, such as uranium-235, are fissile. Washington Post, 28 Apr. 2022 But given Iran’s advancements since the original deal, Tehran is currently enriching uranium at up to 60 percent purity, producing uranium metal, and hiding stockpiles of fissile material from the IAEA. The Editors, National Review, 4 Mar. 2022 This is the ability to put enough pressure on the fissile material to detonate it and create a nuclear yield. CBS News, 5 Jan. 2022 The nation’s output of uranium—a fissile material for nuclear weapons when enriched—is just a fraction of what could be produced, according to new research from Stanford University’s Center for International Security and Cooperation. Timothy W. Martin, WSJ, 4 Nov. 2021 See More

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'fissile.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


borrowed from Latin fissilis "easily split," from fid-, variant stem of findere "to split, cleave" + -tilis "subject to, susceptible to (the action of the verb)" — more at bite entry 1

First Known Use

1661, in the meaning defined at sense 1

Time Traveler
The first known use of fissile was in 1661


Dictionary Entries Near fissile

Cite this Entry

“Fissile.” Dictionary, Merriam-Webster, Accessed 23 Sep. 2023.

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