The quality or state of being dark, dim, or obscure; dimness, haziness, or fogginess; obscurity or cloudiness of perception or understanding.
From Latin caliginosus (dark, misty) plus English -ity suffix, forming an abstract noun. This term evolved in 16th-century English from Latin philosophical and medical vocabulary describing darkness and obscurity.
For a word meaning 'haziness,' caliginosity itself is pretty hazy and archaic—it's exactly the kind of Latinate noun that 17th-century scholars would have loved, turning the feeling of fog into a philosophical property.
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