vexation vs onus

vexation and onus both are nouns.

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

As nouns, onus is a hyponym of vexation; that is, onus is a word with a more specific, narrower meaning than vexation:

Other hyponyms of vexation include bugaboo, burden, encumbrance, incumbrance, load, business.

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