The two words are used to mean the same thing. See:
http://www.ngdc.noaa.gov/seg/geomag/declination.shtml

Declination is also be used to indicate the position of celestial bodies. When so used, it is used in the same way that latititude is used on the surface of the Earth. If the sun has a declination of 18 degrees south, then it is going to be right above 18 degrees south latitude.