There are some further trigonometric functions that are found occasionally. Few people use them, but it avoids confusion if you know what they are.

The chord of an angle θ is the length of a line joining the ends of two radii of a circle of radius 1, and separated by θ. Equivalently, it is the base of an isosceles triangle where the equal sides are of length 1 and the angle between them is θ.

${\displaystyle {\text{chord}}(\theta )=2\sin \left({\frac {\theta }{2}}\right)}$

The versed sine of an angle, vers(θ) = 1-cos(θ).

The haversine or half versed sine of an angle,

${\displaystyle {\text{havers}}(\theta )={\text{hav}}(\theta )={\frac {1}{2}}(1-\cos(\theta ))=\sin ^{2}\left({\frac {\theta }{2}}\right)}$.

The coversed sine of an angle, covers(θ) = 1-sin(θ).