What term refers to a word indicating the chronological order of a composer’s works?

The term that refers to a word indicating the chronological order of a composer's works is "opus." This term, originating from Latin meaning "work," is commonly used in music to assign a number to each composition, thus creating a systematic way to categorize and reference a composer’s output. For example, Beethoven's works are often referred to by their opus numbers, allowing listeners and musicians to identify and discuss specific pieces in the context of the overall timeline of his compositions.

In contrast, the other terms mentioned have different meanings and contexts within music. A phrase relates to a musical idea or segment, analogous to a sentence in language, and does not pertain to chronological organization. Parallel keys describe a relationship between major and minor scales that share the same tonic note but differ in tonality, which is unrelated to the chronological arrangement of works. Lastly, "meno mosso" is a tempo marking indicating to play more slowly, which also does not correlate with how a composer's works are ordered in time. Thus, "opus" is the correct answer in the context of categorizing a composer's works chronologically.