An Etymological Dictionary of Astronomy and Astrophysics

The difference between the observed → color index of a star and the intrinsic color index corresponding to its → spectral type. It indicates the modification brought to a color index by the → interstellar absorption.

Etymology (EN): → color; excess, M.E., from O.Fr., from L. excessus “departure, going beyond,”
p.p. excedere “to depart, go beyond,” from → ex- “out” + cedere “to go, yield.”

Etymology (PE): Fozuni, from afzuni “excess,” afzuni kardan “to exceed bounds,” → add; → color.