Definition of melancholiness in English:
melancholiness
noun ˈmɛlənk(ə)lɪnɪsˈmɛləŋk(ə)linɪs
The condition of being melancholy; a tendency towards melancholy.
Origin
Early 16th century; earliest use found in Thomas Paynell (d.?1564), translator. From melancholy + -ness.