Noun:
1. In Chemistry: An archaic name for a sulfate.
2. Sulfuric acid. Historically known as oil of vitriol.
3.Something highly caustic or severe in effect, as criticism. This is the definition that is most widely used nowadays.
Origin: 1350-1400; Middle English, Latin: from vitreolum meaning "glassy" (descriptive of the glassy appearance of the several metallic sulfates.)