Who coined the term 'tone clusters' in the 1920s?

The term 'tone clusters' was coined by Henry Cowell in the 1920s. Cowell was a pioneering American composer who explored innovative techniques and sounds in music, one of which was the use of tone clusters—groups of pitches that are played simultaneously and are often very close together in terms of intervals. This approach significantly contributed to the development of contemporary music, as it expanded the possibilities of harmony and texture.

Cowell's experiments with tone clusters involved using the entire keyboard of the piano, playing adjacent keys simultaneously, which resulted in unique and often dissonant sonorities. His advocacy for these sounds opened new avenues for composers that followed, influencing movements such as modernism and avant-garde music. Thus, his terminology and concepts helped to define an important aspect of 20th-century composition.

Other composers such as Charles Ives, Olivier Messiaen, and Arnold Schoenberg certainly contributed vastly to the evolution of music in the 20th century, but it was Cowell who specifically introduced and named the concept of 'tone clusters,' cementing his place in music history.