cosine

play
noun co·sine \ˈkō-ˌsīn\

Definition of cosine

  1. 1 :  a trigonometric function that for an acute angle is the ratio between the leg adjacent to the angle when it is considered part of a right triangle and the hypotenuse

  2. 2 :  a trigonometric function cos θ that for all real numbers θ is given by the sum of the alternating series and that is exactly equal to the cosine of an angle of measure θ in radians :  a trigonometric function cos θ that for all real numbers θ is given by the sum of a series of which the first term is 1 and succeeding terms alternate in sign with the kth term consisting of a fraction whose numerator is θ raised to the exponent 2(k - 1) and whose denominator is the factorial of 2(k - 1) and that is exactly equal to the cosine of an angle of measure θ in radians

Origin and Etymology of cosine

New Latin cosinus, from co- + Medieval Latin sinus sine


First Known Use: 1635


COSINE Defined for English Language Learners

cosine

play
noun co·sine \ˈkō-ˌsīn\

Definition of cosine for English Language Learners

  • geometry : the ratio between the long side (called the hypotenuse) and the side that is next to an acute angle in a right triangle


Learn More about cosine


Seen and Heard

What made you want to look up cosine? Please tell us where you read or heard it (including the quote, if possible).

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!

WORD OF THE DAY

a person who is a bore or nuisance

Get Word of the Day daily email!

WORD GAMES

Take a 3-minute break and test your skills!

  • peter-bruegel-tower-of-babel-painting
  • What language does pajama come from?
Name That Thing

Test your visual vocabulary with our 10-question challenge!

TAKE THE QUIZ
Word Winder's CrossWinder

Test Your Knowledge - and learn some interesting things along the way.

TAKE THE QUIZ

Love words? Need even more definitions?

Subscribe to America's largest dictionary and get thousands more definitions and advanced search—ad free!