segment vs length

segment and length both are nouns.

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

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

segment: one of several parts or pieces that fit with others to constitute a whole object
length: a section of something that is long and narrow

Other hyponyms of segment include bend, curve, dado, leaf, straight, straightaway, subdivision, subsection.

segment (noun)	length (noun)
one of several parts or pieces that fit with others to constitute a whole object	a section of something that is long and narrow
one of the parts into which something naturally divides	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

segment (verb)	length (verb)
divide into segments
divide or split up