Definitions
1.nounOriginally a small utility knife for cutting the points of quill feathers or reeds into nibs to provide or repair writing implements in times before pens with artificial nibs, generally metal, became commercially available in the 19th century. Early versions of penknives commonly were small sheath knives.
2.nounA 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.
3.nounAs the need to cut nibs for pens fell away, but small utility pocket-knives remained popular, "penknife" became synonymous with "pocket-knife". Modern penknives often incorporate other tools such as corkscrews, but as a rule are smaller than general-purpose pocketknives.