Webster's Revised Unabridged Dictionary · 1913

Nebulosity

Nebulosity , noun

[Latin nebulositas: compare French nébulosité]

1.
The state or quality of being nebulous; cloudiness; haziness; mistiness; nebulousness.
The nebulosity... of the mother idiom. — I. Disraeli
2.
(a) (Astronomy) The stuff of which a nebula is formed.
(b)
(Astronomy) A nebula.