fastening vs linkage

fastening and linkage both are nouns.

Word	Noun	Adjective	Verb	Adverb
fastening	Yes	No	No	No
linkage	Yes	No	No	No

As nouns, linkage is a hyponym of fastening; that is, linkage is a word with a more specific, narrower meaning than fastening:

Other hyponyms of fastening include bonding, soldering, doweling, earthing, grounding, ligature, tying, welding, fixation.

fastening (noun)	linkage (noun)
the act of fastening things together	the act of linking things together
restraint that attaches to something or holds something in place	a mechanical system of rods or springs or pivots that transmits power or motion
	(genetics) traits that tend to be inherited together as a consequence of an association between their genes; all of the genes of a given chromosome are linked (where one goes they all go)
	an associative relation