meniscus

bow curve half-moon sickle

concave figure convex figure cresentoid demilune horned moon hornlike lune new moon old moon

arc arch contour loop trajectory

ambit bend bight bow camber catenary chord circle circuit circumference compass concavity crook curlicue curvature ellipse festoon flexure hairpin half-moon helix horseshoe hyperbola incurvation incurvature ogee parabola quirk round sinuosity sweep swerve turn vault whorl

curvation rondure

line

glass

contact monocle optic spectacles

bifocal trifocal