The Collaborative International Dictionary of English v.0.48:
Tangent \Tan"gent\, n. [L. tangens, -entis, p. pr. of tangere to
touch; akin to Gr. ? having seized: cf. F. tangente. Cf.
Attain, Contaminate, Contingent, Entire, Tact,
Taste, Tax, v. t.] (Geom.)
A tangent line curve, or surface; specifically, that portion
of the straight line tangent to a curve that is between the
point of tangency and a given line, the given line being, for
example, the axis of abscissas, or a radius of a circle
produced. See Trigonometrical function, under Function.
Artificial tangent, or Logarithmic tangent, the logarithm
of the natural tangent of an arc.
Natural tangent, a decimal expressing the length of the
tangent of an arc, the radius being reckoned unity.
Tangent galvanometer (Elec.), a form of galvanometer having
a circular coil and a short needle, in which the tangent
of the angle of deflection of the needle is proportional
to the strength of the current.
Tangent of an angle, the natural tangent of the arc
subtending or measuring the angle.
Tangent of an arc, a right line, as ta, touching the arc of
a circle at one extremity a, and terminated by a line ct,
passing from the center through the other extremity o.