omission vs exception

omission and exception both are nouns.

Word	Noun	Adjective	Verb	Adverb
omission	Yes	No	No	No
exception	Yes	No	No	No

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

Other hyponyms of omission include inadvertence, oversight, pretermission, elision, exclusion.

omission (noun)	exception (noun)
a mistake resulting from neglect	a deliberate act of omission
neglecting to do something; leaving out or passing over something	an instance that does not conform to a rule or generalization
any process whereby sounds or words are left out of spoken words or phrases	grounds for adverse criticism
something that has been omitted