To subject to the process of removing phlegm or impure watery matter from a substance.
From de- + phlegm + -atize (to treat or subject to a process). A technical term from 17th-19th century chemistry and medicine.
Early scientists tried to dephlegmatize everything—they thought removing water from liquids would reveal hidden properties, which is kind of adorable in hindsight since water is usually what makes things work.
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