According to Joe Gioia in "The Guitar and the New World: A Fugitive History", "the blues" as a term for ennui, depression, or sadness and later a style of music

According to Joe Gioia in "The Guitar and the New World: A Fugitive History", "the blues" as a term for ennui, depression, or sadness and later a style of music (or several, really) comes from the expression blue devil which "first appeared in the early 1600s, coinciding with the dramatic increase in the New World production of indigo dye." He describes the conditions on the indigo plantations as "a hell that would have given Dante pause".