"Plume" can be accepted but we must understand that it is more specific to a "quill", i.e., a sharpened bird-feather, that is dipped into a bottle of ink. For what it's worth, WordReference does not even list "pen" as one of the definitions for "plume". So I think we would have to agree that your assessment is spot on: it is an obsolete term. http://www.wordreference.com/fren/plume It seems that the term "stylo" has captured the scene when it comes to pens. Even a fountain pen is now called a "stylo à encre".