Definition of cosine
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
: a trigonometric function cos θ that for all real numbers θ is given by the sum of the alternating series {latex}1  \frac{x^2}{2!} + \frac{x^4}{4!}  \frac{x^6}{6!} + \frac{x^8}{8!}  \dots{/latex} and that is exactly equal to the cosine of an angle of measure θ in radians
Test Your Vocabulary
Commonly Confused Words Quiz

 I went to the ______ store to buy a birthday card.
Test your visual vocabulary with our 10question challenge!
TAKE THE QUIZA daily challenge for crossword fanatics.
TAKE THE QUIZLove words? Need even more definitions?
MerriamWebster unabridged
Share cosine
Time Traveler for cosine
The first known use of cosine was in 1635
See more words from the same year