Merriam-Webster's Word of the Day


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Build your vocabulary with Merriam-Webster's Word of the Day! Each day a Merriam-Webster editor offers insight into a fascinating new word -- explaining its meaning, current use, and little-known details about its origin.



December 22nd, 2014

Episode 53 of 681 episodes

Merriam-Webster's Word of the Day for December 22, 2014 is: fissile \FISS-ul\ adjective 1 : capable of being split or divided in the direction of the grain or along natural planes of cleavage 2 : capable of undergoing fission Examples: Uranium-235, which is frequently used in making bombs and missiles, is one of the most abundant fissile materials. "These hurdles notwithstanding, during the peak of the program the United States secured an estimated 400 metric tons of fissile material, enough to make several thousand nuclear weapons." Jack Caravelli, Business Insider, November 17, 2014 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") 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.