I have distilled the definition of prototyping, from a UX perspective, not a dictionary one. Anyway, it was part of a three part blog entry on my blog and I would be interested in your feedback and comments.
I divided the definition into two: what the prototype does and what it is. In so doing I have aimed at a definition that will help designers control a prototype rather than the prototype controlling them. It is distilled from the book I co-wrote with Michael Arent and Nevin Berger, Effective Prototyping for Software Makers. Anyway, I would appreciate it if you could look at it and see if it is useful to you.