“What is the name of a triangle with one round side?” December 9, 2016 By Neal Leave a Comment What is the name of a triangle with one round side? Kind of like a piece of cake which has two straight sides and one round side. Or a slice of pizza. -Quora It has properties of a circle with the round part, since it has a section of the circumference. And the area of the shape is a part of an entire circle.