compulsory vs mandatory

compulsory is not a noun while mandatory is a noun.

Word	Noun	Adjective	Verb	Adverb
compulsory	No	Yes	No	No
mandatory	Yes	Yes	No	No

As adjectives, compulsory and mandatory are synonyms defined as:

Other synonyms of compulsory include required.

compulsory (noun)	mandatory (noun)
	a territory surrendered by Turkey or Germany after World War I and put under the tutelage of some other European power until they are able to stand by themselves
	the recipient of a mandate

compulsory (adjective)	mandatory (adjective)
required by rule	required by rule