The evolution of Peirce's semiotics and his doctrine of phenomenological categories resulted in new concepts and in several significant revisions of earlier key terms. The paper examines Peirce's concept of representation and its derivatives (representamen, to represent, representational function, etc.) in their relation to terms and conceptual metaphors such as sign, sign vehicle, embodiment, medium, and mediation. From representation and its derivatives, Peirce gradually shifted his focus of attention to medium and mediation. The paper examines how, why, and when Peirce changed the semantic scope of his terms and why and in which way he used some of them in a broader and a narrower sense at the same time. It argues that major characteristics of Peirce's terminology and scholarly rhetoric have their roots in his ethics of terminology, his theory of scientific writing, and his doctrine of fallibilism.