separateness vs severalty

separateness and severalty both are nouns.

Word	Noun	Adjective	Verb	Adverb
separateness	Yes	No	No	No
severalty	Yes	No	No	No

As nouns, separateness and severalty are synonyms defined as:

Other synonyms of separateness include discreteness, distinctness.

separateness (noun)	severalty (noun)
the quality of being not alike; being distinct or different from that otherwise experienced or known	exclusive individual ownership
political independence	the state of being several and distinct
the state of being several and distinct