Tangent :  (noun)
1: a straight line or plane that touches a curve or curved surface at a point but does not intersect it at that point
2: ratio of the opposite to the adjacent side of a right-angled triangle [syn: tan]

abutter, adjoiner, air line, approach, asymptote, axis, beeline, borderer, bottleneck, bystander, chord, collision course, concentralization, concentration, concourse, concurrence, confluence, conflux, congress, convergence, converging, crossing, diagonal, diameter, direct line, directrix, edge, focalization, focus, funnel, great-circle course, hub, immediate neighbor, looker-on, meeting, mutual approach, narrowing gap, neighbor, neighborer, normal, onlooker, perpendicular, radius, radius vector, right line, secant, segment, shortcut, side, spokes, straight, straight course, straight line, straight stretch, straightaway, streamline, transversal, vector,