Trenchancy

trenchancy [TREN-chən-see]
n. the state or quality of being sharp, incisive, or penetrating, as in words or an argument

[From French trenchier ("to cut")]

More common than the noun trenchancy in ordinary discourse is its adjective form, trenchant ("incisive or keen, as language or a person; cutting"). And more common still is when you cut a whole in the ground, you've dug a trench. It has the same etymology.

In "The Revenge of Karl Marx," Christopher Hitchens, who as a young man called himself a Trotskyite, but has since renounced his former faith, here praises the sharpness of some of Marx's rhetoric:

One pleasure in the rereading of Marx is to savor the trenchancy and aptness of his literary allusions.

Because I don't see or hear trenchancy enough, I'm not sure if the noun is ever employed to mean sarcasm; however, trenchant the adjective at times is -- in the sense that a trenchant remark can be a cutting remark -- used to mean sarcastic.

In this 2004 article for the National Review, William F. Buckley describes some writing by John Kenneth Galbraith as "ironic trenchancy." Perhaps that qualifies as sarcasm?

John Kenneth Galbraith ... has a new book, The Economics of Innocent Fraud, for publication in April. The publishers are dizzy with delight over the brief (62-page) manuscript, in which the author, in his singular way, using an ironic trenchancy that shatters glass with its explosive acuity, makes his briefs.

One interesting historical tidbit on Galbraith, arguably the world's worst famous economist, is that he did his PhD at UC Davis in the early 1930s, where he also served on the faculty. To be perfectly honest, there was no UC Davis, when he was here. Instead, Davis was a branch campus, the School of Agriculture, of UC Berkeley at that time. So Galbraith's PhD. in Agricultural Economics is ultimately from Berkeley, even if he studied in Davis and was a head and a half taller than Milton Friedman (see picture above).