What term refers to a group of notes sung to one syllable of text that highlights key words?

The term that refers to a group of notes sung to one syllable of text, which is designed to highlight key words, is known as melisma. In the context of vocal music, melisma involves the use of several pitches or notes applied to a single syllable, allowing for expressive delivery and emphasizing particular words or themes within the text. This technique is often used in various musical styles, including vocal religious music, opera, and popular song forms, enabling the singer to convey emotion and create a compelling performance.

Other choices, while related to musical concepts, do not match this definition. De capo aria refers to a ternary form commonly used in Baroque operas and oratorios, sonata cycle pertains to a structured organization of movements in instrumental music, and homorhythmic texture describes a musical texture where multiple voices or parts move together in rhythm, which does not specifically involve the concept of syllables being emphasized through multiple notes.