menstruum

noun3

1. •
   Any liquid medium
2. •
   (historical) A solvent.

   • [T]hat combustible sulphureous Body is presently prey'd upon and devoured by the aereal incompassing Menstruum, whose office in this Particular I have shewn in the Explication of Charcole. — 1665
3. •
   [in the plural] (historical) The menses; menstrual discharge.