1 : to leave out (someone or something) : to not include (someone or something)
Example: Please don't omit any details.
Note: This sense of omit is often followed by from. Examples: They omitted your name from the list. You can omit the salt from the recipe. He has been omitted from the pool of candidates.
2 formal : to fail to do (something) ― followed by to + verb ~し忘れる
Examples: I omitted [=(more commonly) neglected] to mention that it was my fault. They omitted to tell us the directions.
neglect to mention that (that以下)のことをきちんと述べない
この2の意味に関しては、Longmanがわかりやすかった。
omit to do something:formal to not do something, either because you forgot or deliberately omit to mention/say/tell etc