* In: This is the most straightforward opposite, meaning "inside" or "part of."
* Included: This emphasizes being a member of a group or set.
* Present: This focuses on existence or being physically located somewhere.
* Among: This implies being part of a collection or group.
For example:
* "The cat is not in the house" could be opposite to "The cat is in the house."
* "The item is not included in the package" could be opposite to "The item is included in the package."
Ultimately, the best opposite of "not in" depends on the specific meaning you want to convey.