Source : Webster's Revised Unabridged Dictionary (1913)

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}, 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.

Tangent \Tan"gent\, a. [L. tangens, -entis, p. pr.]
   Touching; touching at a single point; specifically (Geom.)
   meeting a curve or surface at a point and having at that
   point the same direction as the curve or surface; -- said of
   a straight line, curve, or surface; as, a line tangent to a
   curve; a curve tangent to a surface; tangent surfaces.

   {Tangent plane} (Geom.), a plane which touches a surface in a
      point or line.

   {Tangent scale} (Gun.), a kind of breech sight for a cannon.
      

   {Tangent screw} (Mach.), an endless screw; a worm.

Source : WordNet®

tangent
     n 1: a straight line or plane that touches a curve or curved
          surface at a point but does not intersect it at that
          point
     2: ratio of the opposite to the adjacent side of a right-angled
        triangle [syn: {tan}]