\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.
Note: 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.