The most spherical or round of all things.
Spheriest is a fun word that makes people think of balls, planets, and other round things.
Examples:
The basketball is the spheriest ball.
The Earth is the spheriest planet in our solar system.
The spheriest object in the room is the marble.
The spheriest fruit is the orange.
The spheriest animal is the hedgehog.
The spheriest thing in the universe is a perfect sphere.