tangent

Etymology

Borrowed from Latin tangentem, the accusative of tangēns (“touching”) (in the phrase līnea tangēns (“a touching line”)), the present participle of the verb tangō (“touch”, verb), from Proto-Italic *tangō, from Proto-Indo-European *teh₂g- (“to touch”). Cognate with Old English þaccian (“to touch lightly, pat, stroke”). More at thack, thwack.

noun

1. (differential geometry) A straight line touching a curve at a single point without crossing it there.
2. (mathematics) 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. A topic nearly unrelated to the main topic, but having a point in common with it.
   I believe we went off onto a tangent when we started talking about monkeys on unicycles at his retirement party.
   “Uncle Barnaby was always father and mother to me,” Benson broke in; then after a pause his mind flew off at a tangent. “Is old Hannah all right—in the will, I mean?” 1928, Lawrence R. Bourne, chapter 1, in Well Tackled!
   2009: Stuart Heritage, Hecklerspray, Friday the 22ⁿᵈ of May in 2009 at 1 o’clock p.m., “Jon & Kate Latest: People You Don’t Know Do Crap You Don’t Care About” Jon & Kate Plus 8 is a show based on two facts: (1) Jon and Kate Gosselin have eight children, and (2) the word ‘Kate’ rhymes with the word ‘eight’. One suspects that if Kate were ever to have another child, a shady network executive would urge her to put it in a binbag with a brick and drop it down a well. But this is just a horrifying tangent.
4. (art) 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. (music) A small metal blade in a clavichord that strikes the strings to produce sound.

adj

1. (geometry) Touching a curve at a single point but not crossing it at that point.
2. Of a topic, only loosely related to a main topic.
3. (rail transport, of track) Straight; not horizontally curved.
   The collision occurred on a two-mile stretch of tangent track.