S: (n) straight line (straight_line%1:25:00::) (a line traced by a point traveling in a constant direction; a line of zero curvature) "the shortest distance between two points is a straight line"
S: (n) asymptote (asymptote%1:25:00::) (a straight line that is the limiting value of a curve; can be considered as tangent at infinity) "the asymptote of the curve"
S: (n) tangent (tangent%1:25:00::) (a straight line or plane that touches a curve or curved surface at a point but does not intersect it at that point)
S: (n) radius (radius%1:25:00::) (a straight line from the center to the perimeter of a circle (or from the center to the surface of a sphere))
S: (n) diameter (diameter%1:25:00::) (a straight line connecting the center of a circle with two points on its perimeter (or the center of a sphere with two points on its surface))