Other forms: penknives
A penknife is a small folding blade carried in a pocket. A little penknife, open the penknife, whittle with a penknife.
The name is literal: it was the knife for cutting and shaping a quill pen, and a scribe sharpened one constantly. Carrying a folding blade under three inches is lawful in Britain, and anything longer or locking is not.
1nounpenknifeA small folding blade carried in a pocket.
“He cut the string with the penknife he always kept in his pocket.”
penknife is a knife.
Pen plus knife, from the knife used to cut and trim a quill pen.
Middle English
penne knyfe
English, today
penknife
From Middle English penne knyfe; equivalent to pen + knife. In the original sense, named for its purpose: aiding the use of a (traditional) ink pen through the following tasks: trimming the tip of a quill pen, trimming a reed for a nib, and (in some cases) allowing erasure by scraping away some ink.
Etymology from Wiktionary, CC BY-SA