/ Dictionary / Index S spectral line: Meaning and Definition of Find definitions for: spec'tral line' Pronunciation: [key] — Optics. Optics. a line in a spectrum due to the absorption or emission of light at a discrete frequency. Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease. spectral spectral series Related Content Daily Word Quiz: endear Analogy of the Day: Today’s Analogy Spelling Bee: Today’s Spelling Bee Frequently Misspelled Words Frequently Mispronounced Words Easily Confused Words Writing & Language