Sea
The unconscious at its full scale — what you can stand at the edge of, but never fully see.
The sea in a dream is the unconscious in its largest form. A calm sea is your inner life at rest. A storm at sea is the inner life turned over.
Wading at the edge of the sea is the most common version of the dream — you are present at the edge of something vast in yourself, willing to feel it but not swimming out. Swimming far from shore is a confidence in your own depth that the dream wants you to remember on waking.
Where you often see it. The sea at the edge of a beach. The sea in a storm. The sea in unnatural calm. The dream uses the sea for the unconscious at its full scale — what you can stand at the edge of but never fully see.
What it is not. The sea is not danger by default. Its state at the moment of the dream is the reading.
Related in the dictionary. Read sea with beach (the boundary), ship, boat, and any scene where scale exceeds what you can hold.