lunar caustic
noun [mass noun] Chemistry, archaic
Silver nitrate, especially fused in the form of a stick.For a long time in the treatment of places to be cauterized, only the dreaded nitrate of lunar caustic was used to produce the caustic effect....
- At the time with which we are concerned lunar caustic was used as an astringent, in medicine and for cosmetic purposes, and for marking linen.
Origin
Early 19th century: lunar in the sense 'containing silver'.