Figure of Speech
Synaesthesia
From Greek syn (together) + aisthesis (sensation). Championed by Baudelaire ('Correspondances') and Rimbaud; a defining feature of Symbolist and Romantic imagery.
Definition
The description of one sense in terms of another — the cross-wiring of sensory domains in poetic imagery.
Example
Keats: 'Heard melodies are sweet, but those unheard / Are sweeter' — sound perceived as taste.