x1 is an object that has a shape that is three-dimensional and has an axis (especially of symmetry and/or along which cross-sections are mutually similar), or which is approximately a figure of revolution, or which is approximately the result of taking a two-dimensional shape and sweeping it along a curve in a constant way; x1 is (nearly) cylindrical and is made of/has composition x2, having geometric/topological properties x3.
x1 (line segment) is a neuein/neusis line segment (line element) constructed from directrix x2 (curve; not necessarily linear) to catchline x3 (curve; not necessarily linear, despite the name) which is inclined toward pole x4 (point) such that it has diastema (length) x5 (li; nonnegative extended-real number).
x1 (linear manifold, vector, etc.) is/lies secant to x2 (object, surface, curve, manifold, etc.) passing through or toward points/loci x3 (set of intersected points), by standard/definition/in system x4.
x1 is orthogonal/perpendicular/right/at right angle/rectified/square/normal to x2, where they (are projected to) intersect orthogonally at locus/on set x3, otherwise being utterly distinct (and not even on the same axis/scale) in sense x4