altitude vs ALT

altitude and ALT both are nouns.

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

As nouns, altitude and ALT are synonyms defined as:

altitude and ALT: angular distance above the horizon (especially of a celestial object)

Other synonyms of altitude include EL, elevation.

altitude (noun)	ALT (noun)
elevation especially above sea level or above the earth's surface	angular distance above the horizon (especially of a celestial object)
angular distance above the horizon (especially of a celestial object)
the perpendicular distance from the base of a geometric figure to the opposite vertex (or side if parallel)