Penknife, or pen knife, is a small folding knife. Today penknife is also the common British English term for both a pocketknife, which can have single or multiple blades, and for multi-tools, with additional tools incorporated into the design.
Originally, penknives were used for thinning and pointing quills (cf. penna, Latin for feather) to prepare them for use as dip pens and, later, for repairing or re-pointing the nib. A penknife might also be used to sharpen a pencil, prior to the invention of the pencil sharpener. In the mid-1800s, penknives were necessary to slice the uncut edges of newspapers and books.
A penknife did not necessarily have a folding blade, but might resemble a scalpel or chisel by having a short, fixed blade at the end of a long handle.
During the 20th century there has been a proliferation of multi-function pocketknives with assorted blades and gadgets, the most famous of which is the Swiss Army knife, referred to in British English as penknives.
A larger folding knife than a penknife, especially one in which the blade locks into place as a protection, as for skinning animals, is referred to by some as a claspknife.
upon your knee with the back of a penknife,
As he came along in the train, he had been sharpening a pencil, and the sudden jolt of the engine as it drew up at a station had driven the penknife against his face...