penknife

noun, plural pen·knives.

1. a small pocketknife, formerly one used for making and sharpening quill pens.

noun plural -knives

1. a small knife with one or more blades that fold into the handle; pocketknife

n.early 15c., from pen (n.1) + knife (n.). So called because such small knives were used to sharpen quills.