singing vs solmization

singing and solmization both are nouns.

Word	Noun	Adjective	Verb	Adverb
singing	Yes	Yes	No	No
solmization	Yes	No	No	No

As nouns, solmization is a hyponym of singing; that is, solmization is a word with a more specific, narrower meaning than singing:

singing: the act of singing vocal music
solmization: singing using solfa syllables to denote the notes of the scale of C major

singing (noun)	solmization (noun)
the act of singing vocal music	singing using solfa syllables to denote the notes of the scale of C major
disclosing information or giving evidence about another	a system of naming the notes of a musical scale by syllables instead of letters

singing (adjective)	solmization (adjective)
smooth and flowing