If something is superthick, it is much thicker than usual.
Superthick can make people think of big, heavy, or hard to move.
Examples:
The book is superthick.
The sandwich is superthick with cheese.
The superthick fog made it hard to see.
Her hair is superthick and hard to brush.
The superthick walls kept the noise out.
The superthick ice didn't melt in the sun.