Diffuseness, n.
The quality of being diffuse; especially, in writing, the use of a great or excessive number of word to express the meaning; copiousness; verbosity; prolixity.
Shades of meaning
Fernald has no entry of its own for diffuseness; he lists it under circumlocution.
Where he writes about it:
Etymologically, diffuseness is a scattering, both of words and thought; redundancy is an overflow. — from circumlocution