From elusive + -ness.
elusiveness (usually uncountable, plural elusivenesses)
- The state of being elusive.
1954, Alexander Alderson, chapter 1, in The Subtle Minotaur[1]:Slowly she turned round and faced towards a neat white bungalow, set some way back from the path behind a low hedge of golden privet. No light showed, but someone there was playing the piano. The strange elusiveness of the soft, insistent melody seemed to draw her forward.