permanence vs length

permanence and length both are nouns.

Word	Noun	Adjective	Verb	Adverb
permanence	Yes	No	No	No
length	Yes	No	No	No

As nouns, length is a hypernym of permanence; that is, length is a word with a broader meaning than permanence:

Other hypernyms of permanence include duration.

permanence (noun)	length (noun)
the property of being able to exist for an indefinite duration	a section of something that is long and narrow
	the linear extent in space from one end to the other; the longest dimension of something that is fixed in place
	continuance in time
	the property of being the extent of something from beginning to end
	size of the gap between two places