in keyboard music of the Baroque period, a short grace note sounded together with the principal note or chord, but quickly released
See acciaccatura in American Heritage Dictionary 4
(ä-chäˌkə-to͝orˈə)
noun Music
An ornament note that is one half step or one whole step below a principal note and is sounded at the same time as the principal note, adding dissonance to a harmony.