A small pocketknife; originally used to cut quill pens WordNet 3.0 & Open English WordNet

Penknife, or pen knife, is a small folding knife. Wikipedia

Small folding knife Wikidata

A small knife designed for safe and convenient storage, typically in the form of a miniature clasp knife, or with blade retractable into the handle. For the most part, such more convenient designs eventually replaced rigid pen knives in cutting quill pens or sharpening pencils. Wiktionary