fastness vs fixedness

fastness and fixedness both are nouns.

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

As nouns, fastness and fixedness are synonyms defined as:

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

Other synonyms of fastness include fixity, fixture, secureness.

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