lxxviii vs seventy-eight

lxxviii is not a noun while seventy-eight is a noun.

Word	Noun	Adjective	Verb	Adverb
lxxviii	No	Yes	No	No
seventy-eight	Yes	Yes	No	No

As adjectives, lxxviii and seventy-eight are synonyms defined as:

Other synonyms of lxxviii include 78.

lxxviii (noun)	seventy-eight (noun)
	a shellac based phonograph record that played at 78 revolutions per minute
	the cardinal number that is the sum of seventy and eight

lxxviii (adjective)	seventy-eight (adjective)
being eight more than seventy	being eight more than seventy