Mēn'strŭ-ūm, n.

n.; Eng. pl. MĒN'STRŬ-ŪMS; Lat. pl. MĒN'STRŬ-A. [Lat. menstruus. See supra.] Any fluid or subtilized substance which dissolves a solid body; a solvent.

Inquire what is the proper menstruum to dissolve a 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 of this word is supposed to have originated in some notion of the old chemists about the influence of the moon in the preparation of dissolvents.” Johnson.