noun
An enclosure (enclosed area) used to contain domesticated animals, especially sheep or cattle.
There are two steers in the third pen.
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.
The bullpen.
Two righties are up in the pen.
verb
To enclose in a pen.
Watching where shepherds pen their flocks at eve.
noun
A tool, originally made from a feather but now usually a small tubular instrument, containing ink used to write or make marks.
He took notes with a pen.
Please use a pen, not a pencil, when filling out this form. Use black or blue ink only.
A writer, or their style.
He has a sharp pen.
those learned pens
Marks of ink left by a pen.
He's unhappy because he got pen on his new shirt.
A light pen.
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.