penknife

from WordNet (r) 3.0 (2006)

penknife
    n 1: a small pocketknife; originally used to cut quill pens

from The Collaborative International Dictionary of English v.0.48

Penknife \Pen"knife`\, n.; pl. {Penknives}. [Pen + knife.]
   A small pocketknife; formerly, a knife used for making and
   mending quill pens.
   [1913 Webster]