means A handheld instrument that lays down ink to write or draw; also a small enclosure for animals or, informally, a prison.

from The writing tool comes from Latin 'penna,' meaning feather or wing — back when a pen really was a sharpened quill plucked from a bird, dipped in ink and scratched across the page. The other 'pen,' the animal enclosure, is a separate Old English word ('penn') of uncertain root, and the slang for prison is simply a clipping of 'penitentiary.' Three pens, two unrelated families, one humble spelling.