An asymptote
An asymptote is a straight line which a curve approaches arbitrarily closely as they head towards infinity.
A straight line which is approached , but never reached by an infinite branch of a curve , and which can be regarded as a line tangent to the curve at infinity.
Considering an asymptote as a tangent to the curve "at infinity", the asymptote is the straight line itself.
No, it would not.
The set of points on a straight curve that extends to infinity in both directions is a line. A ray is the set of points that lie on a straight curve that is terminated at a point, and continues to infinity. It is also called a half-line. If the set is terminated at a point at both ends, then it is a line segment.
Your question seems very confused. The normal convention of the Cartesian coordinate system would place negative numbers below the x axis, so that any curve approaching negative infinity would curve downward, not upward.
An asymptote of a curve is a line where the distance of the curve and line approach zero as they tend to infinity (they get closer and closer without ever meeting) If one zooms out of a hyperbola, the straight lines are usually asymptotes as they get closer and closer to a specific point, yet do not reach that point.
They curve with the curve of the Earth.
Curve is one possible opposite of straight if straight refers to line that does not bend. Other meanings of straight like honest, heterosexual, and direct have different opposites than curve.
a curve... Well that could be an answer however it is not possible to have a bend or a curve 'in' a straight road. A curve or bend is, by definition, after the end of one straight section and before the beginning of the next; so it can not be 'in' a straight road.
Below the diode's Forward Voltage (Vf) typically 0.7V, the curve is at (roughly) zero. At around 0.5 it begins to curve upward, and at around 0.7V, the voltage drop is almost constant (the curve heads straight upwards to infinity). See link.
The straight ball.