Synesthesia
Etymology
A modern compound from Greek syn-, "together," and aisthesis, "sensation," on the model of anaesthesia — literally "sensation together." It was adopted in the late nineteenth century for the perceptual phenomenon in which stimulating one sense automatically stimulates another. Critics borrowed it for the poetic technique that fuses sense-impressions in language.
noun · /sin-us-THEE-zhuh/
The blending of the senses, so that one kind of sensation triggers another.
What it names
Both the neurological condition of tasting shapes or seeing letters in color, and the literary device of describing one sense through another — “a loud shirt,” “a sweet melody” — naming the crossing of sensory wires.
Example
For her, synesthesia is literal: every Tuesday is a deep russet brown, and the number seven is faintly bitter.
Related idea
Synesthesia fuses two senses together; a metaphor carries meaning across from any domain to another, sensory or not.