The quality of being physically caustic; burning, corrosive.
1996, Christopher J. Biermann, Handbook of Pulping and Papermaking, Academic Press, 3.8 Kraft Pulping, p. 89, https://books.google.ca/books?id=sfZfyEmqs_AC&printsec=frontcover#v=onepage&q&f=false
Causticity is the ratio of NaOH to active alkali (as always both chemicals are on an Na₂O basis), expressed as a percentage.
(figuratively) Being caustic in speech, humour etc.
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