synaesthesia
noun
°A physiological or psychological phenomenon whereby a particular sensory stimulus triggers a second kind of sensation. For example, reading the letter 'r' may trigger the visual sensation of the colour purple in the mind or the eye of the synaesthete (grapheme → colour synaesthesia); or, more rarely, for example, the phoneme /l/ may elicit the taste of mince (lexical → gustatory synaesthesia).
°A literary device whereby one kind of sensation is described in the terms of another.