The story
From being produced by the action of the Doppler effect on individual atoms and molecules.
Etymology from Wiktionary, CC BY-SA 4.0.
Doppler broadening
Today it means: The broadening of the spectral lines of a high-temperature or rapidly-rotating object due to redshifting of spectral lines from atoms and molecules moving away from the observer and blueshifting of spectral lines from atoms and molecules moving toward the observer. Full definition →