dead reckoning vs approximation

dead reckoning and approximation both are nouns.

Word	Noun	Adjective	Verb	Adverb
dead reckoning	Yes	No	No	No
approximation	Yes	No	No	No

As nouns, approximation is a hypernym of dead reckoning; that is, approximation is a word with a broader meaning than dead reckoning:

Other hypernyms of dead reckoning include estimate, estimation, idea.

dead reckoning (noun)	approximation (noun)
navigation without the aid of celestial observations	the act of bringing near or bringing together especially the cut edges of tissue
an estimate based on little or no information	the quality of coming near to identity (especially close in quantity)
	an approximate calculation of quantity or degree or worth
	an imprecise or incomplete account