0 A pure substance is not mixed with anything else. -- чистый, неразбавленный
1 used to emphasize that a feeling, quality, or state is completely and only that thing -- чистейший, полнейший
pure coincidence
3 the study of mathematics/physics, etc based only on ideas and not on practical use -- чистая математика/теоретическая физика и т. д.
4 completely good and not having any bad qualities or bad morals -- безупречный