Definition of poison pen in English:

poison pen

adjective

  • Designating, of, or relating to a letter or letters written anonymously and with malicious, libellous, or abusive intent.

noun

  • A writer of a poison-pen letter. Also: a pen dipped in poison (used allusively with reference to the virulent style of writing characteristic of a poison-pen letter).

Origin

Early 20th century; earliest use found in Evening Post (Frederick, Maryland). From poison + pen.

Pronunciation

poison pen

/ˌpɔɪzn ˈpɛn/