Which term indicates 'with an added octave' in Italian music terminology?

The term that indicates 'with an added octave' in Italian music terminology is "col." This term is often used in musical scores to instruct performers to play or sing a part in conjunction with the octave interval, enhancing the richness and depth of the music.

In various contexts, "col" can be followed by other indications that specify the exact nature of the accompaniment, such as "col piano" or "col legno," which relate to the style of performance. However, when referring specifically to an octave, "col" signifies that the notes should be played or sung with an octave added, leading to a fuller sound.

The other options refer to different musical expressions or instructions. "Con brio" means to perform vigorously and with spirit, conveying energy. "Coll'" is a contraction of "con il," which means "with the" in English, and typically precedes another term. "Con grazia" translates to "with grace," indicating a light, flowing performance. Each of these terms highlights different musical qualities but does not specifically denote the idea of playing with an added octave.