General alternatives:
* Equivalent
* Analogue
* Counterpart
* Alternative
* Paraphrase
* Substitution
* Similar word
* Near synonym
* Near equivalent
* Close synonym
More specific alternatives:
* Antonym (opposite meaning)
* Hypernym (broader category)
* Hyponym (specific category)
* Meronym (part of a whole)
* Holonym (whole containing a part)
Informal alternatives:
* Same thing
* Other word for it
* Different word for the same thing
* Another way to say it
The best alternative depends on the specific situation and what you're trying to communicate.
For example, if you're talking about two words that have almost the same meaning, but not exactly the same, you might use "near synonym" or "close synonym." If you're talking about two words that have completely opposite meanings, you would use "antonym."