"Di" as in Dihedral means two as in the two angles of the standard wings. When the airplane is sitting level. Each wing is angled up. There are "di" (two) angles.

"Poly" means many. More than two. It could be 3 or mor angles. And they don't always have to be in the same direction like on the Corsair.

By the way, the Corsair has a shape that is known as an "Inverted Gull" wing.