S: (n) straight line (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) geodesic, geodesic line ((mathematics) the shortest line between two points on a mathematically defined surface (as a straight line on a plane or an arc of a great circle on a sphere))
W: (v) bound [Related to: bound] (place limits on (extent or amount or access)) "restrict the use of this parking lot"; "limit the time you can spend with your friends"
S: (n) limit, bound, boundary (the greatest possible degree of something) "what he did was beyond the bounds of acceptable behavior"; "to the limit of his ability"