The word for today is…
fissile (adjective):
1: capable of or prone to being split or divided in the direction of the grain or along natural planes of cleavage
2: capable of undergoing fission
Source : Merriam -Webster
Etymology : 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 as being fissile, as it splits readily into thin slabs.
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