noun which may take the genitive case particle 'no', na-adjective, noun
coldhearted; pitiless; merciless; heartless
Describes a person or action lacking compassion or mercy. Can be used as a noun or adjectivally with な or の.
彼は情け知らずの男だ。
He is a heartless man.
I can't believe you'd say such a pitiless thing.