tangent

Short definition from Wiktionary

Noun

1. 1
   A straight line touching a curve at a single point without crossing it there.
2. 2
   A function of an angle that gives the ratio of the sine to the cosine, in either the real or complex numbers. Symbols: tan, tg.
3. 3
   A topic nearly unrelated to the main topic, but having a point in common with it.
4. 4
   A visual interaction between two or more lines or edges that creates a perceived relationship between them, often in a way that the artist did not intend.
5. 5
   A small metal blade in a clavichord that strikes the strings to produce sound.

Adjective

1. 1
   Touching a curve at a single point but not crossing it at that point.
2. 2
   Of a topic, only loosely related to a main topic.
3. 3
   Straight; not horizontally curved.