Syn-es-the-sia n. Physiol. Sensation produced at a point other than or remote from the point of stimulation, as of a color from hearing a certain sound (fr. Gk, syn = together + aisthesis = to perceive). Synesthesia is an involuntary joining in which the real information of one sense is accompanied by a perception in another sense. In addition to being involuntary, this additional perception is ...