vitriolic (vi-tree-OL-ik) adjective
Extremely caustic; bitterly scathing.
[From Latin vitrum (glass).]
Sulfuric acid, a highly corrosive substance, was formerly known as oil of vitriol or simply vitriol. It was named vitriol owing to the glassy appearance of its salts.
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"Unlike many other districts in Ventura County, Simi Valley has suffered a steady diet of noisy board meetings, vitriolic letters to the editor and name-calling directed at board members."
-- Mack Reed; Simi Schools in Throes of Tumult, Hope; Los Angeles Times; Jun 2, 1996.