1. A state characterized by a lack of awareness, unconsciousness.
2. A state characterized by a lack of awareness of ongoing internal processes.
3. In the depth psychologies, especially psychoanalysis, a domain of the psyche encompassing the repressed id functions, the primitive impulses and desires, the memories, Content/images and wishes that are too anxiety-provoking to be accepted into consciousness.
(Arthur S. Reber: Dictionary of Psychology, Penguin 1985)

1. The ground of all existence, combining the spiritual principle of nature, will, and reason. The notion was developed by K.R.E. von Hartmann (1842-1906)... synthesizing the theories of Schelling, Schopenhauer, and Hegel. The misery of existence is explained by the suffering of the unconscious from the constant strife between will and reason; it can be alleviated only by conscious reason gaining ascendancy over blind impulse, until the final liberation of the unconscious at the end of physical life.
2. A source of influences on behavior. In Freud's theory, it is the container of memories of experiences that are repressed in personal consciousness, as a consequence of habits, developed from childhood, of denying impulses that might occasion disapproval. Such repressed impulses persist as unconscious wishes and often adversely influence personality development.
Jung distinguished between the personal and the collective unconscious; the latter contains 'archetypes' or symbols representing inherited ways of responding to particular types of experience. Man's basic drive is towards self-realization; freedom is attainable through assimilation of the unconscious by consciousness.
(Antony Flew: A Dictionary of Philosophy, St. Martin's Press 1979)

see also Collective Unconscious.

1. The process of comprehending something, of appreciating the meaning of a word, sentence, event, proposition, etc.
2. An elusive intuitive process whereby one succeeds in apprehending the deep significant meaning of an event, a concept, an idea, etc.
3. A sympathetic appreciation for another person, particularly for their point of view on some matter or their belief on some issue.
4. In older writings, a hypothesized mental faculty the function of which was to yield comprehension of the meanings of things.
(Arthur S. Reber: Dictionary of Psychology, Penguin 1985)

Verstehen, allg. soviel wie begreifen, insbes. im Gegensatz zum Erklären und Begründen das intuitive Erfassen des Sinns, des Wesens eines "Gegenstandes" aus ihm selbst heraus. Verstehen in dieser Bedeutung setzt die innere Verwandtschaft mit dem zu verstehenden Gegenstand voraus. Die Möglichkeit des Verstehens ist darin begründet, dass alles seelisch-geistige Leben sich in mehr oder weniger festen Formen äussert, die etwas ausdrücken, etwas bedueten. Die Notwendigkeit des Verstehens ergibt sich aus der Tatsache, dass solche Äusserungen etwas Individuelles, Einmaliges, Einzigartiges darstellen, für das allgemeine Regeln oder Gesetze nicht anwendbar, bzw. nicht zureichend sind.
So heisst Versthen nach Spranger "geistige Zusammenhänge in der Form objektiv gültiger Erkenntnis als sinnvoll auffassen". Die Wissenschaft vom Wesen und von den Formen des Verstehens heisst Hermeneutik.
(J. Hoffmeister: Wörterbuch der Philosophischen Begriffe, Meiner Verlag, 1955)