[1] : The Collaborative International Dictionary of English v.0.48

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.
   1913 webster

   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.
      1913 webster
      1913 webster
see also:
tangent plane tangent scale tangent screw 

[2] : WordNet (r) 2.0

tangent plane
     n : the plane that contains all the lines tangent to a specific
         point on a surface

Plane >> P Words
Plane, definition of term: Plane
plane_pag1.html

Plane Table >> P Words
Plane Table, definition of term: Plane Table
plane+table_pag1.html

Jack Plane >> J Words
Jack Plane, definition of term: Jack Plane
jack+plane_pag1.html

Inclined Plane >> I Words
Inclined Plane, definition of term: Inclined Plane
inclined+plane_pag1.html

Ground Plane >> G Words
Ground Plane, definition of term: Ground Plane
ground+plane_pag1.html