1718, "capable of seeing spectres;" 1815, "ghostly;" from spectre + -al (1). Meaning "pertaining to a spectrum" is 1832, from stem of spectrum + -al (1). Related: Spectrally.
spectral analysis
spectral colors
spectral emanations
spectacles
spectacular
spectate
spectator
specter
spectral
spectre
spectro-
spectrogram
spectrograph
spectrometer
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