Within the depth-psychology corpus, ‘vapor’ operates simultaneously as a cosmological, physiological, and psychological concept, drawing on ancient Greek medicine, Renaissance Neoplatonism, and alchemical philosophy. The term names a liminal substance — neither fully corporeal nor purely spiritual — that mediates between body and soul, matter and mind. Ficino, as reconstructed by Thomas Moore, inherits the physicians’ definition of spirit as ‘a certain vapor of the blood, pure, subtle, hot and lucid,’ a formulation that places vapor at the threshold of the sensible and the psychic. James Hillman, reading alchemical sources through Trinick, locates vapor as the ‘thick white vapour’ medium of the coniunctio, the dissolving agent that dissolves gender polarity and enables psychic conjunction. In von Franz’s commentary on the Aurora Consurgens, the Latin equivalence of vapor, spiritus, and anima — ‘sic Opus nostrum nihil aliud est quam vapor et aqua’ — makes the term axiomatic for alchemical psychology as a whole. Hillman’s Anima further identifies the vaporous soul-substance with anima itself: dew, mist, and cool exhalation clustering around psychic concepts of wetness and indirection. Caswell and Onians trace the etymological kinship of Greek thumos with ‘smoke and vapor,’ grounding psychological concepts of spirit and breath in material volatility. The convergence of these traditions makes vapor a master-trope for the subtle body, the anima-medium, and the transformative middle region of psychic work.