8. enigmatic

The word enigmatic is an adjective referring to something being an enigma. The word "Enigma" was the name of the German enciphering machine used by the Axis powers during World War II. At this time it was thought that this system of ciphering was impossible to decode, thus transforming the word into describing something as either puzzling or inexplicable in occurrence or situation. For example, the Mona Lisa can be described as enigmatic because her facial expression is unknown.

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Miller Humphreys