General antonyms:
* Same
* Similar
* Alike
* Identical
* Consistent
More specific antonyms:
* Uniform (referring to a lack of variety)
* Consistent (referring to a lack of change)
* Matching (referring to two things being exactly the same)
Example:
* Different: The two houses are different in size and style.
* Antonym: The two houses are identical in size and style.
It's important to consider the specific meaning of "different" in your context to choose the most appropriate antonym.