This paper is a contribution to research on iconicity and diagrammatic transparency in the lexicon. The focus lies on the potential contribution of polysemy to iconicity that is generally neglected by iconicity researchers. The three Peircean icon types of images, diagrams and metaphors are scrutinised with respect to their relationship to polysemy. It is shown that polysemy is diagrammatic and also closely connected to Peircean metaphor, since the icon types of metaphor and diagrams considerably overlap. Consequently, polysemy also plays a role in diagrammatic transparency and therefore must be considered as a distinct degree on scales of diagrammatic transparency. Existing scales of diagrammatic transparency should be revised. The most important problem with them is that they concentrate on the formal part of word transparency and neglect the semantic part of transparency issues. Evidence from questionnaire studies on lexical motivation suggests that diagrammatic transparency is not only a formal issue, but strongly depends on the semantic relation connecting a stimulus and its motivational base. Stimuli that are related by metaphorical similarity to a potential motivational partner are perceived more easily as motivated than stimuli that are potentially motivated by contiguity.