omission vs aphaeresis

omission and aphaeresis both are nouns.

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

As nouns, aphaeresis is a hyponym of omission; that is, aphaeresis 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
aphaeresis: (linguistics) omission at the beginning of a word as in `coon' for `raccoon' or `till' for `until'

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

omission (noun)	aphaeresis (noun)
a mistake resulting from neglect	(linguistics) omission at the beginning of a word as in `coon' for `raccoon' or `till' for `until'
neglecting to do something; leaving out or passing over something
any process whereby sounds or words are left out of spoken words or phrases
something that has been omitted