Without being fully aware or deliberately thinking about it; in a way that happens in your mind below the level of consciousness.
From Latin 'sub-' (under/below) + 'conscious' (aware). Popularized in the late 1800s as psychology developed the concept of the unconscious mind with Freud and others.
Before Freud, people didn't really have a word for the automatic mental processes that happen below awareness—the entire concept of your brain doing things 'behind your back' is basically a 150-year-old idea that changed psychology forever.
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