onus vs concern

onus and concern both are nouns.

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

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

Other hypernyms of onus include headache, vexation, worry.

onus (noun)	concern (noun)
an onerous or difficult concern	something that interests you because it is important or affects you
	something or someone that causes anxiety; a source of unhappiness
	a feeling of sympathy for someone or something
	an anxious feeling
	a commercial or industrial enterprise and the people who constitute it

onus (verb)	concern (verb)
	be relevant to
	be on the mind of