Etymology: Latin tangent-, tangens, present participle of tangere to touch; perhaps akin to Old English thaccian to touch gently, stroke
a. meeting a curve or surface in a single point if a sufficiently small interval is considered <straight line tangent to a curve> b. (1) having a common tangent line at a point <tangent curves> (2) having a common tangent plane at a point <tangent surfaces> 2. diverging from an original purpose or course ; irrelevant <tangent remarks> II. noun Etymology: New Latin tangent-, tangens, from linea tangens tangent line Date: 1594 1. a. the trigonometric function that for an acute angle is the ratio between the leg opposite to the angle when it is considered part of a right triangle and the leg adjacent b. a trigonometric function that is equal to the sine divided by the cosine for all real numbers θ for which the cosine is not equal to zero and is exactly equal to the tangent of an angle of measure θ in radians 2. a line that is tangent; specifically a straight line that is the limiting position of a secant of a curve through a fixed point and a variable point on the curve as the variable point approaches the fixed point 3. an abrupt change of course ; digression <the speaker went off on a tangent> 4. a small upright flat-ended metal pin at the inner end of a clavichord key that strikes the string to produce the tone
New Collegiate Dictionary. 2001.