I have owned dozens of penknives, but never till now stopped to think why they are so called.

"As a means towards his composure and self-possession, he entered into a more minute examination of the office than he had yet had time to make; looked into the wig-box, the books, and ink-bottle; untied and inspected all the papers; carved a few devices on the table with a sharp blade of Mr Brass's penknife; "

penknife ['pɛnˌnaýf]
noun
(plural: -knives)
a small knife with one or more blades that fold into the handle; pocketknife
[ETYMOLOGY: 15th Century: so called because it was originally used for making and repairing quill pens]