Real Dictionary

mordant
Mordant humour is very critical and often mocks someone or something.

mordant in American English
a substance used in dyeing to fix the coloring matter, as a metallic compound that combines with the organic dye to form an insoluble colored compound, or lake, in the fiber of the fabric
biting, cutting, caustic, or sarcastic, as speech, wit, etc.
to treat or impregnate with a mordant
adjective: sharply caustic or sarcastic, as wit or a speaker; biting
noun: a substance used in dyeing to fix the coloring matter, esp. a metallic compound, as an oxide or hydroxide, that combines with the organic dye and forms an insoluble colored compound or lake in the fiber
transitive verb: to impregnate or treat with a mordant

mordant in British English
adjective: sarcastic or caustic
noun: a substance used before the application of a dye, possessing the ability to fix colours in textiles, leather, etc
verb: to treat (a fabric, yarn, etc) with a mordant