1. (n.) A straight line (or the length of such line) connecting any point, as of a curve, with a fixed point, or pole, round which the straight line turns, and to which it serves to refer the successive points of a curve, in a system of polar coordinates. See Coordinate.

2. (n.) An ideal straight line joining the center of an attracting body with that of a body describing an orbit around it, as a line joining the sun and a planet or comet, or a planet and its satellite.

aeronautics air lane air route air service airway astronautics aviation axis ballooning beeline blind flying chord cloud-seeding commercial aviation contact flying corridor cruising cut cutoff diagonal diameter direct line directrix edge flight flying general aviation gliding great-circle course lane normal path perpendicular pilotage radius radius vector right line sailing sailplaning secant segment shortcut shortest way side soaring straight straight course straight line straight stretch straightaway streamline tangent transversal vector winging