from The American Heritage® Dictionary of the English Language, 4th Edition
- n.pl. A set of several hundred dark lines appearing against the bright background of the continuous solar spectrum and produced by absorption of light by the cooler gases in the sun's outer atmosphere at frequencies corresponding to the atomic transition frequencies of these gases.
from the GNU version of the Collaborative International Dictionary of English
- plural proper n. The lines of the spectrum; especially and properly, the dark lines of the solar spectrum, so called because first accurately observed and interpreted by Fraunhofer, a German physicist.
After Joseph von Fraunhofer (1787-1826), German physicist.(American Heritage® Dictionary of the English Language, Fourth Edition)