noun
vicious pen; poison pen
Refers to writing that is malicious, slanderous, or sharply critical, often in journalism or literature. The word itself is somewhat literary and not an everyday term.
彼の毒筆は多くの政治家を震え上がらせた。
His poison pen made many politicians tremble.
そのコラムニストは毒筆で知られている。
That columnist is known for his vicious pen.