1. cruel and bitter criticism.
2. sulfuric acid.
late Middle English (denoting the sulfate of various metals): from Old French, or from medieval Latin vitriolum, from Latin vitrum
definition via google.com
Where I came across the word:
“The ecumenical councils which gave rise to the Creed were stormy events, in which truth and error struggled against each other with sometimes sharp invective and vitriol.”
Eckardt, Burnell, F. Jr. The New Testament in His Blood: A Study of the Holy Liturgy of the Christian Church. 2010. Print. (Kewanee, Ill.: Gottesdienst)