Mordant
Etymology
From French mordant, the present participle of mordre, "to bite," from Latin mordere, "to bite" (also behind "morsel" and "remorse"). The literal sense of "biting" carried directly into English for wit and criticism that bite. The same word names the chemical mordant that "bites" dye into fabric — another survival of the root’s original meaning.
adjective · /MOR-dunt/
Sharply and often bitterly sarcastic, in a way that is incisive rather than merely cruel.
What it names
The bite of wit that draws a little blood — criticism so sharp and well-aimed it stings even as you admire it.
Example
Her mordant review dismantled the novel in three sentences that were funnier than anything in the book.
Related idea
Caustic wit burns and is chiefly meant to wound; mordant wit bites too, but tends to be sharper, cleverer, and more precisely aimed.
noun · /MOR-dunt/
A substance used in dyeing that fixes a color to a fabric so it will not wash out.
What it names
The chemical — often a metallic salt such as alum — that bonds a dye to fibers, and the similar agent used to fix stains in microscopy.
Example
Alum was the most common mordant, biting the dye deep into the wool.
Related idea
The word means "biting" in French, which links both senses: a mordant wit bites into its target, and a mordant bites the dye into the cloth.