"spectral" in the adjective sense
1. spectral
of or relating to a spectrum
"spectral colors"
"spectral analysis"
2. apparitional, ghostlike, ghostly, phantasmal, spectral, spiritual
resembling or characteristic of a phantom
"a ghostly face at the window"
"a phantasmal presence in the room"
"spectral emanations"
"spiritual tappings at a seance"
Source: WordNet® (An amazing lexical database of English)
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