grandson

As nouns the difference between grandson and cush

is that grandson is a son of one's child while cush is shortened form of cushion, the soft lip around the edge of the table that allows the balls to bounce cleanly.

As an adjective cush is

excellent, very good.

As a proper noun Cush is

the son of Ham and grandson of Noah, progenitor of the African peoples.

As a noun grandson

is a son of one's child.

As an adjective grandsonless is

(rare) without a grandson.