General Synonyms:
* Unmixed
* Unpolluted
* Immaculate
* Unsullied
* Untainted
* Unblemished
* Perfect
* Absolute
* Genuine
* Authentic
Synonyms for "pure" in the context of morality or ethics:
* Virtuous
* Chaste
* Innocent
* Honest
* Upright
* Moral
Synonyms for "pure" in the context of substances:
* Uncontaminated
* Undiluted
* Unadulterated
* Refined
* Unprocessed
Other Synonyms:
* Clear
* Simple
* Basic
* Fundamental
The best synonym to use will depend on the specific context and the nuance you want to convey.