pure has 19 distinct synonyms spread across 3 of its 7 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. Its one recorded opposite is impure.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
free of extraneous elements of any kind
“pure air and water”
without qualification; used informally as (often pejorative) intensifiers
“an arrant fool”
(of color) being chromatically pure; not diluted with white or grey or black
(used of persons or behaviors) having no faults; sinless
“I felt pure and sweet as a new baby”
2 of the 7 recorded senses carry no synonym, antonym or related term, so they are not shown above. Every sense, with its definition and examples, is on the full entry for pure.
Synonyms, antonyms and the broader and narrower relations for pure come from Princeton University’s WordNet. Full sources and licences.