menstrua

Webster's Dictionary (GCIDE)

Menstruum \Men"stru*um\, n.; pl. E. Menstruums, L. Menstrua. [L. menstruus. See Menstruous.] Any substance which dissolves a solid body; a solvent. [1913 Webster]

The proper menstruum to dissolve metal. --Bacon. [1913 Webster]

All liquors are called menstruums which are used as dissolvents, or to extract the virtues of ingredients by infusion or decoction. --Quincy. [1913 Webster]

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. [1913 Webster]