Originally: a case of metal, leather, etc., for holding pens; a pen-case. Later also: a writing case.

A person who pens or composes a piece of writing, a document, a statement, etc.; a writer of something (either the original composer, or a copier).

A person who pens cattle. Also (chiefly Australian and NZ): a person who pens sheep ready for the shearers in a shearing shed (frequently as "penner-up").