https://www.collinsdictionary.com/dictionary/english/solfeggio music
1. a voice exercise in which runs, scales, etc, are sung to the same syllable or syllables
2. solmization, esp the French or Italian system, in which the names correspond to the notes of the scale of C major
solmization
https://www.collinsdictionary.com/dictionary/english/solmization music
a system of naming the notes of a scale by syllables instead of letters derived from the 11th-century hexachord system of Guido d'Arezzo, which assigns the names ut (or do), re, mi, fa, sol, la, si (or ti) to the degrees of the major scale of C (fixed system) or (excluding the syllables ut and si) to the major scale in any key (movable system)