An Etymological Dictionary of Astronomy and Astrophysics

In an atom, a characteristic amount of energy radiated (as line emission) when an electron moves from an outer orbit to an inner orbit around the nucleus, corresponding to the lost energy of the electron.

Etymology (EN): From L. emissionem “a sending out,” from emiss-, stem of emittere “send forth,” from → ex- “out” + mittere “to send.”

Etymology (PE): Gosil, variant gosi “sending away, dismission;” Mid.Pers. wisé “to despatch” (Parthian Mid.Pers. wsys- “to despatch;” Buddhist Mid.Pers. wsydy “to despatch;” Sogdian ‘ns’yd- “to exhort”), from Proto-Iranian *vi-sid- “to despatch, send off,” from prefix vi- “apart, away, out,” + *sid- “to call.”