Old term for solvent. [Mediev. L. menstrual fluid, thought to possess certain solvent properties, ntr. of L. menstruus, monthly]
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men·stru·um 'men(t)-strə(-wə)m n, pl -stru·ums or -strua -str(ə-w)ə a substance that dissolves a solid or holds it in suspension: SOLVENT
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men·stru·um (menґstroo-əm) [L. menstruus menstruous: it was long believed that the menstrual fluid had a peculiar solvent quality] a solvent medium.Medical dictionary. 2011.