length vs transience

length and transience both are nouns.

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

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

length (noun)	transience (noun)
a section of something that is long and narrow	an impermanence that suggests the inevitability of ending or dying
the linear extent in space from one end to the other; the longest dimension of something that is fixed in place	the attribute of being brief or fleeting
continuance in time
the property of being the extent of something from beginning to end
size of the gap between two places