de·mon·ol·o·gy noun alsodae·mon·ol·o·gy\-jē\ (-es) Etymology:demon, daemon + -o- + -logy 1.: a branch of learning that deals with demons or with popular beliefs in or superstitions about demons or evil spirits; also: a treatise on demons or on beliefs in demons 2.: belief in demons; specifically: a systematized religious doctrine of evil spirits