onus vs vexation

onus and vexation both are nouns.

Word	Noun	Adjective	Verb	Adverb
onus	Yes	No	No	No
vexation	Yes	No	No	No

As nouns, vexation is a hypernym of onus; that is, vexation is a word with a broader meaning than onus:

Other hypernyms of onus include concern, headache, worry.

onus (noun)	vexation (noun)
an onerous or difficult concern	the act of troubling or annoying someone
	something or someone that causes anxiety; a source of unhappiness
	anger produced by some annoying irritation
	the psychological state of being irritated or annoyed