Origin: L. Menstruus. See Menstruous.
Any substance which dissolves a solid body; a solvent. The proper menstruum to dissolve metal. (bacon) All liquors are called menstruums which are used as dissolvents, or to extract the virtues of ingredients by infusion or decoction. (Quincy)
The use is supposed to have originated in some notion of the old chemists about the influence of the moon in the preparation of dissolvents. The monthly discharge of blood from the uterus of nonpregnant women from puberty to menopause; the women were sickly and subject to excessive menstruation; a woman does not take the gout unless her menses be stopped.