The distinction between subconscious and unconscious is a subtle one. The noun subconscious refers to the mind’s activities just beneath consciousness, and the part of the mind devoted to such activities. The unconscious, by contrast, is the part of the mind that exerts a strong influence on behavior but is not noticed by one’s consciousness.
And what does consciousness mean, anyway? Conscious is ultimately from the Latin verb conscire, meaning “be aware” or “know,” and consciousness refers to the state of awareness or knowledge. The terms are used both in the conventional sense of being in a conscious state—not asleep or unconscious—and in the spiritual sense of being aware of more than just one’s basic physical existence, of being attuned to something greater than what is immediately apparent.
Unconscious, too, has two disparate meanings: If one is asleep or one’s mind has been affected by medication or injury so that one is unaware of one’s surroundings, one is said to be unconscious. But one can also be described as unconscious when one behaves in a manner that is not self-reflective or that demonstrates an obliviousness to one’s environment, as when a person acts rudely without seeming to recognize the unfortunate behavior or mindlessly damages or pollutes.
The root of the terms is scire, meaning “know”; it is, as you may have guessed, also the source of science. Other terms that derive from this root include conscience, which refers to the part of your mind that serves as a moral compass, and self-conscious, which originally referred neutrally to self-awareness but now can connote acting in a deliberate manner but usually refers to a preoccupation with how one is perceived by others, generally because of insecurity.
Semiconscious means “only partially awake or aware,” and preconscious is a psychoanalytical term that refers to a thought or idea that one is not conscious of but that can be recalled without hesitation because one does not repress or resist the thought. Conscient, meanwhile, is a rare variant of conscious.
The adjective unsconscionable pertains to a lack of regard for one’s conscience and therefore of regard for other people or for things in offensive or oppressive behavior; its antonym, conscionable, is obsolete.