magnetic variation vs magnetic declination

magnetic variation and magnetic declination both are nouns.

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

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

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

Other synonyms of magnetic variation include variation.

magnetic variation (noun)	magnetic declination (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