The antonyms for the word "Curvation" are "straightness," "rigidity," "flatness," "linearity," and "unbendingness." These words describe the absence of curves or bends in an object or surface. "Straightness" denotes the quality of being a straight line or devoid of any curvature. "Rigidity" connotes a stiffness or inflexibility in movement or form. "Flatness" indicates a lack of bumps or irregularities in a surface or structure. "Linearity" suggests a quality of being arranged or aligned in a straight line or direction. And "unbendingness" implies an inability to bend or flex in any way.