The categorization of individuals or groups as social parasites has often been treated as an example of semantic transfer from the biological to the social domain. Historically, however, the scientific uses of the term parasite cannot be deemed to be primary, as their emergence in the seventeenth and eighteenth centuries was preceded by a much older tradition of religious and social terminology. Its social use in modern times, on the other hand, builds on a secondary metaphorization from the scientific source concept. This article charts the history of the term parasite from its etymological origins to the present day, distinguishes its metaphorical and non-metaphorical uses, and discusses the implications of these findings regarding the cognitive understanding of the relationship between (perceived) literal and metaphorical meanings. In conclusion, it is argued that metaphorization needs to be analyzed not only in terms of its conceptual structure but also in its role in discourse history.