The crossword solution for the term 'LACKING A KEY, MUSICALLY' is 'ATONAL', which has 6 letters. ATONAL music is a type of music that does not conform to any key or tonality, meaning it does not have a tonal center or key signature. It is often considered to be dissonant and chaotic, and is usually composed using twelve-tone technique. ATONAL music is often used in modern classical music, as well as in some forms of jazz and experimental music.