Synaesthesia: A rhetorical trope involving shifts in imagery. It
involves taking one type of sensory input (sight, sound, smell,
touch, taste) and comingling it with another separate sense in
an impossible way. In the resulting figure of speech, we end up
talking about how a color sounds, or how a smell looks. When we
say a musician hits a 'blue note' while playing a sad song, we
engage in synaesthesia. When we talk about a certain shade of
color as a 'cool green,' we mix tactile or thermal imagery with
visual imagery the same way. When we talk about a 'heavy
silence,' we also use synaesthesia. Examples abound: The scent
of the rose rang like a bell through the garden. 'I caressed the
darkness with cool fingers.' French poets, especially Baudelaire
in Les fleurs du mal, have proven especially eager to use
synaesthesia. The term itself is a fairly late addition to
rhetoric and literary terminology, first coined in 1892, though
examples of this figure of speech can be found in Homer,
Aeschylus, Donne, Shelley,