WordNet records no synonym and no antonym for line spectrum. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a spectrum in which energy is concentrated at particular wavelengths; produced by excited atoms and ions as they fall back to a lower energy level
Synonyms, antonyms and the broader and narrower relations for line spectrum come from Princeton University’s WordNet. Full sources and licences.