mordant

(noun) a substance used to treat leather or other materials before dyeing; aids in dyeing process.

(adj) harshly ironic or sinister. Synonyms: black, grim. Examples: "Black humor." "A grim joke." "Grim laughter." "Fun ranging from slapstick clowning ... to savage mordant wit."

(adj) of a substance, especially a strong acid; capable of destroying or eating away by chemical action. Synonyms: caustic, corrosive, erosive, vitriolic.