noun

• (slang) A penitentiary, i.e. a state or federal prison for convicted felons.
  "They caught him with a stolen horse, and he wound up in the pen again."
• (baseball) The bullpen.
  "Two righties are up in the pen."

verb

• (transitive) To enclose in a pen.
  "Watching where shepherds pen their flocks at eve."

noun

• (figurative) A writer, or their style.
  "He has a sharp pen."
• (colloquial) Marks of ink left by a pen.
  "He's unhappy because he got pen on his new shirt."
• (zoology) The internal cartilage skeleton of a squid, shaped like a pen.
  "A pen is nothing more complex than a decalcified shell, so one mutation of the genes that controlled calcification could be all it took."
• (now rare, poetic, dialectal) A feather, especially one of the flight feathers of a bird, angel etc.
  "And eke the pennes, that did his pineons bynd, Were like mayne-yards, with flying canuas lynd, With which whenas him liſt the ayre to beat […]"

verb

• (transitive) To write (an article, a book, etc.).
  "Prying open the crate, you discover a carefully wrapped, handwritten copy of one of Matriarch Dilinaga's treatises. It is unlikely she penned it herself, but the flowing brushwork and intricate watercolor illustrations clearly show the hand of a master scribe."