3. The _Sine_ of an angle, or of an arc, is a line drawn from one end of
an arc, perpendicular to a diameter drawn through the other end.
4. The _Cosine_ of an arc is the perpendicular distance from the center
of the circle to the sine of the arc; or, it is the same in magnitude as
the sine of the complement of the arc.
5. The _Tangent_ of an arc is a line touching the circle in one
extremity of the arc, and continued from thence, to meet a line drawn
through the center and the other extremity.
6. The _Cotangent_ of an arc is the tangent of the complement of the
arc. The _Co_ is but a contraction of the word complement.
7. The _Secant_ of an arc is a line drawn from the center of the circle
to the extremity of the tangent.