Definition of pen:

part of speech: verb

To confine in a pen or in a narrow place; to coop; to incage.

part of speech: verb

To write; to compose and commit to paper; to indite.

part of speech: noun

An instr. for writing, formerly almost wholly of quills, now commonly of metal.

part of speech: noun

A small enclosure for sheep, fowls, & c.; a coop; a reservoir for water.