Omission

n. deletion; negligence; failure; default

Omission is, in Catholic teaching, the failure to do something one can and ought to do. If this happens advertently and freely a sin is committed. The degree of guilt incurred by an omission is measured like that attaching to sins of commission, by the dignity of the virtue and the magnitude of the precept to which the omission is opposed as well as the amount of deliberation.
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Noun
1. a mistake resulting from neglect
(synonym) skip
(hypernym) mistake, error, fault
(hyponym) failure
(derivation) exclude, except, leave out, leave off, omit, take out
2. something that has been omitted; "she searched the table for omissions"
(hypernym) neglect, disuse
3. any process whereby sounds are left out of spoken words or phrases
(synonym) deletion
(hypernym) linguistic process
(hyponym) aphaeresis, apheresis
4. neglecting to do something; leaving out or passing over something
(hypernym) disregard, neglect
(hyponym) oversight, inadvertence
(derivation) neglect, pretermit, omit, drop, miss, leave out, overlook, overleap

n. omission, oversight

(n.)
The act of omitting; neglect or failure to do something required by propriety or duty.
  

(n.)
That which is omitted or is left undone.