Men″stru‐um (?), n.; pl. E. Menstruums (#), L. Menstrua (#). [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. Johnson.