2.NounThe act of neglecting to perform an action one has an obligation to do.
"E&O insurance (for errors and omissions) covers both errors of commission and errors of omission."
3.NounAn instance of those acts, or the thing left out thereby; something deleted or left out.
"The suspicious omissions in the new edition of the book attracted claims of censorship."
4.NounSomething not done or neglected.
"The lack of a sponge count was an omission by the surgical team."
5.NounThe shortening of a word or phrase, using an apostrophe ( ' ) to replace the missing letters, often used to approximate the sound of speech or a specific dialect.