pneu·ma·tol·o·gy \-jē, -ji\noun (-es) Etymology: New Latin pneumatologia, from pneumat- + -logia -logy 1. a.: the doctrine or theory of spiritual beings (as the Holy Spirit and spirits between God and man) b. (1): the doctrine of spiritual phenomena (2): magical or necromantic lore 2.archaic: a theory of the nature and functions of mind and soul : psychology 3.archaic: the science of air or gases