n. (Philosophy) a philosophical theory or attitude having various interpretations, generally emphasising the existence of the individual as a unique agent with free will and responsibility for his or her own acts, though living in a universe devoid of any certain knowledge of right and wrong; from one's plight as a free agent with uncertain guidelines may arise feelings of anguish. Existentialism is concerned more with concrete existence rather than abstract theories of essences; is contrasted with rationalism and empiricism; and is associated with Kierkegaard, Heidegger and Sartre, as well as others. [ PJC ]