From The Collaborative International Dictionary of English v.0.48 [gcide]:
Dimness \Dim"ness\, n. [AS. dimness.]
1. The state or quality ? being dim; lack of brightness,
clearness, or distinctness; dullness; obscurity.
[1913 Webster]
2. Dullness, or want of clearness, of vision or of
intellectual perception. --Dr. H. More.
Syn: Darkness; obscurity; gloom. See Darkness.
[1913 Webster]
From WordNet (r) 3.0 (2006) [wn]:
dimness
n 1: the state of being poorly illuminated [syn: dimness,
duskiness]
2: the property of lights or sounds that lack brilliance or are
reduced in intensity [syn: dimness, subduedness]
3: the quality of being dim or lacking contrast [syn: dimness,
faintness]