omission vs elision

omission and elision both are nouns.

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

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

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

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

omission: any process whereby sounds or words are left out of spoken words or phrases
elision: omission of a sound between two words (usually a vowel and the end of one word or the beginning of the next)

Other hyponyms of omission include aphaeresis, apheresis, aphesis, eclipsis, ellipsis.

omission (noun)	elision (noun)
a mistake resulting from neglect	a deliberate act of omission
neglecting to do something; leaving out or passing over something	omission of a sound between two words (usually a vowel and the end of one word or the beginning of the next)
any process whereby sounds or words are left out of spoken words or phrases
something that has been omitted