Secant is a straight line that intersects a curve at two or more points
A tangent line is a line that is parallel to and intersecting a point on a curve, where the limit of the distance between two points on that curve (one of them being the point in question) and those two points also being on that line approaches zero. Since a straight line has only one slope, at all points on the line, then there can only be one tangent line to a straight line, and the tangent line is the same line as the straight line.
Line
If you translate (move without rotation) a copy of the line towards the curve, the first point where the line touches the curve (the tangent to the curve with the slope of the original line) will be the point on the curve closest to the line. Draw a connecting line from this tangent point to the original line, intersecting that original line at right angles. Measure the connecting segment. It is the shortest distance. Vector analysis will give a mathematically strict solution, I do not have the ability to explain this in sufficient detail.
Diameter.
If you take two distinct points on a curve, the arc is the part of the curve connecting the two points while the chord is the straight line connecting them.
A straight line that intersects a circle or curve at two points, but which has both end points outside the circle or curve is called a secant. A straight line that links two points on a circle or curve is called a chord. A straight line which touches a circle or curve at one point is called a tangent. A straight line that cuts a circle or curve at one point is a straight line.* For moving diagrams see Related links below this box.
You had us baffled at "straight curve" . Could you mean if you start at the north pole, walk in a straight line, you will eventually get back to the north pole and round in a circle. Hence a straight line but no end points.
Secant is a straight line that intersects a curve at two or more points
A geometrical curve is defined as any set of points. Therefore, counter-intuitively, a straight line is also a geometrical curve.
A line is a straight path connecting two points and continuing on in both directions past the points. If it starts and ends only at the points then it is a line segment.
A tangent line is a line that is parallel to and intersecting a point on a curve, where the limit of the distance between two points on that curve (one of them being the point in question) and those two points also being on that line approaches zero. Since a straight line has only one slope, at all points on the line, then there can only be one tangent line to a straight line, and the tangent line is the same line as the straight line.
A chord.
Line
A straight line connecting two points on the circumference of a circle
It is a straight line joining two different points on a curve which does not cross the curve between those two points.
Diameter is the length of a straight line passing through the center of a circle or sphere and connecting two points on the circumference of the circle or the surface of the sphere. Circumference is the length of the closed curve of a circle.