An Etymological Dictionary of Astronomy and Astrophysics

1. Angular distance (symbol δ) from the celestial equator. One of the coordinates, with → right ascension, that defines the position of a heavenly body in the equator system. Declination is measured positively (+) north or negatively (-) south of the celestial equator from 0° to 90°.
   
2. Angle between geographic North and magnetic North (symbol D).

See also: Verbal noun of → decline; → -tion.