indisposition vs sickness

indisposition and sickness both are nouns.

Word	Noun	Adjective	Verb	Adverb
indisposition	Yes	No	No	No
sickness	Yes	No	No	No

As nouns, sickness is a hypernym of indisposition; that is, sickness is a word with a broader meaning than indisposition:

indisposition: a slight illness
sickness: impairment of normal physiological function affecting part or all of an organism

Other hypernyms of indisposition include illness, malady, unwellness.

indisposition (noun)	sickness (noun)
a certain degree of unwillingness	impairment of normal physiological function affecting part or all of an organism
a slight illness	the state that precedes vomiting
	defectiveness or unsoundness