length vs fundamental quantity

length and fundamental quantity both are nouns.

Word	Noun	Adjective	Verb	Adverb
length	Yes	No	No	No
fundamental quantity	Yes	No	No	No

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

length: the linear extent in space from one end to the other; the longest dimension of something that is fixed in place
fundamental quantity: one of the four quantities that are the basis of systems of measurement

Other hypernyms of length include physical property, dimension, fundamental measure.

length (noun)	fundamental quantity (noun)
a section of something that is long and narrow	one of the four quantities that are the basis of systems of measurement
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