‘Unclean spirit’ occurs only once in the OT (Zech. 13.2 rûaḥ haṭṭumʾâ, lit. ‘the spirit of impurity’) and 21 times in the NT in both singular and plural. It is found only in the synoptic gospels and Acts and twice in Rev. The related phrase ‘evil spirit’ (pneuma ponēron) occurs in the OT (Evil spirit of God) and eight times in the NT. Often the noun daimonion is used synonymously (see below and Demon).
The belief in supernatural non-corporeal beings considered not to be god…