Meaning of lunar caustic in English:

lunar caustic

noun

mass noun archaic Chemistry
  • 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’.