Menstruum
Menstruum , noun
[Latin menstruus. See Menstruous.]
Any substance which dissolves a solid body; a solvent.
The proper menstruum to dissolve metal.
All liquors are called menstruums which are used as dissolvents, or to extract the virtues of ingredients by infusion or decoction.
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.