magnetic declination vs magnetic variation

magnetic declination and magnetic variation both are nouns.

Word	Noun	Adjective	Verb	Adverb
magnetic declination	Yes	No	No	No
magnetic variation	Yes	No	No	No

As nouns, magnetic declination and magnetic variation are synonyms defined as:

magnetic declination and magnetic variation: the angle (at a particular location) between magnetic north and true north

Other synonyms of magnetic declination include variation.

magnetic declination (noun)	magnetic variation (noun)
the angle (at a particular location) between magnetic north and true north	the angle (at a particular location) between magnetic north and true north