simplicity -
freedom from difficulty or hardship or effort; "he rose through the ranks with apparent ease"; "they put it into containers for ease of transportation"; "the very easiness of the deed held her back"
simplicity -
Freedom from artificial ornament, pretentious style, or luxury; plainness; as, simplicity of dress, of style, or of language; simplicity of diet; simplicity of life.
simplicity -
Freedom from subtlety or abstruseness; clearness; as, the simplicity of a doctrine; the simplicity of an explanation or a demonstration.
Simplicity is a more qualitative word connected to simple. It is a property, condition, or quality which things can be judged to have. It usually relates to the burden which a thing puts on someone trying to explain or understand it.