To free from phlegm; to purify a liquid or substance by removing watery or impure matter.
From de- + phlegmate, combining de- (remove) with the medical term for treating excess phlegm. Used in chemistry and medicine from the 16th-19th centuries.
Alchemists and early chemists used 'dephlegmate' to describe removing water from spirits and oils—it's basically distillation, and they were creating the techniques that became modern chemistry.
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