Synaesthesia (synesthesia): Generally, a neurological condition or psychological process whereby one kind of sensory stimulus evokes the subjective experience of another. For instance, you might perceive music in terms of color, or the sight of ants might make you feel itchy. As a literary technique, synaesthesia is the association of two or more senses in the same image, with one sensation being related in terms of another.
EXAMPLES: To speak of coal as “red hot” associates color (sight) with heat (touch); other common examples include “frigid tone” and “heavy silence.” The first line of the following excerpt from Dame Edith Sitwell’s “Trio for Two Cats and a Trombone” (1922) associates three senses, describing sight (“light”) in terms of touch (“hard”) and sound (“braying”):
The hard and braying light
Is zebra’d black and white… .
The titles of the Red Hot Chili Peppers’ song “Taste the Pain” (1989) and Holly Payne’s novel The Sound of Blue (2005) are examples of synaesthesia, as is the following passage from Anthony Doerr’s novel All the Light We Cannot See (2014):
Piano chords loll in the speaker of the wireless in the guard station, projecting rich blacks and complicated blues down the hall toward the key pound. Church bells send arcs of bronze careening off the windows.