The opposite of "re-occurred" is "never occurred" or "first-time occurrence". Re-occurrence indicates that an event has happened before and is happening again, while lack of recurrence denotes that it has not happened before. Therefore, antonyms of re-occurrence are words like original, new, fresh, uncharted, and unprecedented. Another synonym for the antonym of re-occurrence is rarity. This means that an event or situation is not common and does not happen often. For instance, a person who has never experienced a particular ailment before is said to be experiencing it for the first time instead of it re-occurring.