If מוּדָעוּת is awareness or consciousness, תַּת-מוּדָעis the subconscious or the unconscious. The particle -תַּת means sub- or under-, just as in English, in phrases like:
תַּת-יַמִּי – underwater
תַּת-מִין – subspecies
תַּת-אָלוּף – brigadier general (subservient to the general)
An example of תת-מודע:
זִיגְמוֹנְד פְּרוֹיד פִּתֵּחַ אֶת הַמֻּשָּׂג שֶׁל הַתַּת-מוּדָע.
Sigmund Freud developed the concept of the unconscious.
Although, strictly speaking, the unconscious should be called תת-הַמודע, since תת-מודע is almost a single word on its own, it’s more appropriate to say הַתת-מודע.
Note that here unconscious refers to the psychological phenomenon, not the state of being unconscious of what’s going around around due to injury, etc. That is חֲסַר הַכָּרָה.
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