If something is seaweedy, it is like or has the qualities of seaweed, which is a plant that grows in the sea.
Seaweedy can make people think of the ocean, the beach, or the smell of the sea.
Examples:
The beach was covered in seaweedy plants.
The water was dark and seaweedy.
The seaweedy smell filled the air.
I don't like the taste of seaweedy food.
The seaweedy monster came out of the water.
The seaweedy plants swayed in the ocean currents.