Pen

A pen is a writing instrument which applies ink to some surface.

Originally the word meant quill, and is derived from pinna (Latin for feather. This is because early pens were made from goose feathers by carving the feather with a penknife.

Types of pens currently in use include the ballpoint pen, the fine-line marker pen, the artist's pen, and the fountain pen.

Pens may also be known, although not very commonly, as frindles. This word was invented by the author Andrew Clements in his novel Frindle, the premise of which is that a schoolboy decides to call pens "frindles" and the usage becomes common throughout America.

Things that could be mentioned here

invention of the cartridge pen
invention of the biro
the space pen
the (possibly urban-mythical) tale of the Russians using a pencil in space instead
contrast with brush

A pen is also the term used for the much-reduced and entirely internal shell of some cephalopod mollusks, especially squid.

Pen is also used as a verbal expression of "to create" or "to write".

For example: "Today, I think I'll pen the Great Canadian Novel."

Pen is also used to describe an enclosed location.

For example: Pigpen

Short for penitentiary.