semichord

Semichord is a term found in music theory, used historically to describe a “half chord”—a pitch collection that functions like a traditional triad but is missing one component. In older theoretical writings, a semichord may refer to a two-note sonority whose intervallic content suggests a triad, such that adding a missing tone would complete the triadic harmony. Because two-note sonorities are today more commonly called dyads, the term semichord is largely historical and not widely used in contemporary analysis.

In practice, the concept is used to describe different situations. One sense is a dyadic sonority that strongly implies a triad by its intervallic structure (for example, a root and third or a root and fifth) but lacks one member. Another sense is a fragment of a larger chord where some voices are omitted for voice-leading or timbral reasons, yet the underlying harmonic function remains tied to a triad. The idea is largely about describing incomplete sonorities that still convey triadic intent.

Because semichord lacks a single standardized definition, scholars typically prefer more precise terms such as dyad, triad fragment, or incomplete chord, and they specify the harmonic function or voice-leading context. The term appears in discussions of historical harmony, late-Romantic practice, and certain modern analyses where composers omit chord members for expressive or spectral reasons.