length vs altitude

length and altitude both are nouns.

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

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

length: size of the gap between two places
altitude: the perpendicular distance from the base of a geometric figure to the opposite vertex (or side if parallel)

Other hyponyms of length include leg, arm's length, gauge, light time, skip distance, wingspan, wingspread, wingspread.

length (noun)	altitude (noun)
a section of something that is long and narrow	elevation especially above sea level or above the earth's surface
the linear extent in space from one end to the other; the longest dimension of something that is fixed in place	angular distance above the horizon (especially of a celestial object)
continuance in time	the perpendicular distance from the base of a geometric figure to the opposite vertex (or side if parallel)
the property of being the extent of something from beginning to end
size of the gap between two places