The evolution of the concept of synesthesia in the nineteenth century as revealed through the history of its name

Synesthesia is a rare perceptual condition causing unusual sensations, which are triggered by the stimulation of otherwise unrelated modalities (e.g., the sensation of colors triggered when listening to music). In addition to the name it takes today, the condition has had a wide variety of designations throughout its scientific history. These different names have also been accompanied by shifting boundaries in its definition, and the literature has undergone a considerable process of change in the development of a term for synesthesia, starting with "obscure feeling" in 1772, and ending with the first emergence of the true term "synesthesia" or "synæsthesiæ" in 1892. In this article, we will unpack the complex history of this nomenclature; provide key excerpts from central texts, in often hard-to-locate sources; and translate these early passages and terminologies into English.