fixedness vs fastness

fixedness and fastness both are nouns.

Word	Noun	Adjective	Verb	Adverb
fixedness	Yes	No	No	No
fastness	Yes	No	No	No

As nouns, fixedness and fastness are synonyms defined as:

fixedness and fastness: the quality of being fixed in place as by some firm attachment

Other synonyms of fixedness include fixity, fixture, secureness.

fixedness (noun)	fastness (noun)
the quality of being fixed in place as by some firm attachment	a strongly fortified defensive structure
the quality of being fixed and unchangeable	a rate (usually rapid) at which something happens
remaining in place	the quality of being fixed in place as by some firm attachment