n. the personification of death and the brother of Hypnos (sleep) in Greek mythology, whose name was chosen by Sigmund Freud to designate a theoretical set of strivings oriented toward the reduction of tension and life activity (see death instinct). In Freud’s dual instinct theory, Thanatos is seen as involved in a dialectic process with Eros (love), the striving toward sexuality, continued development, and heightened experience (see life instinct). See also nirvana principle.