Unclean spirit
In English translations of the Bible, unclean spirit is a common rendering of Greek pneuma akatharton (πνεῦμα ἀκάθαρτον; plural pneumata akatharta (πνεύματα ἀκάθαρτα)), which in its single occurrence in the Septuagint translates Hebrew ruaḥ tum'ah (רוּחַ טוּמְאָה).
The Greek term appears 21 times in the New Testament in the context of demonic possession. It is also translated into English as spirit of impurity or more loosely as "evil spirit." The Latin equivalent is spiritus immundus.
The association of physical and spiritual cleanliness is, if not universal, widespread and continues into the 21st century: "To be virtuous is to be physically clean and free from the impurity that is sin," notes an article in Scientific American published 10 March 2009. Some scholarship seeks to differentiate between "unclean spirit" and "evil spirit" (pneuma ponêron) or "demon" (daimonion).