La función verseno (en Latín, sinus versus o sagitta, flecha) es una función trigonométrica que se define con la ecuación

versin(θ)=1−cos⁡(θ)=2 sen2(θ2){\displaystyle {\textrm {versin}}(\theta )=1-\cos(\theta )=2\ {\text{sen}}^{2}\left({\frac {\theta }{2}}\right)\,}Existen tres funciones relacionadas con el verseno: 
El coverseno:

coversin(θ)=versin(π2−θ)=1−sen(θ){\displaystyle {\textrm {coversin}}(\theta )={\textrm {versin}}\left({\frac {\pi }{2}}-\theta \right)=1-{\text{sen}}(\theta )\,}El semiverseno:

semiversin(θ)=versin(θ)2=sen2(θ2){\displaystyle {\textrm {semiversin}}(\theta )={\frac {{\textrm {versin}}(\theta )}{2}}={\text{sen}}^{2}\left({\frac {\theta }{2}}\right)}El semicoverseno:

semicoversin(θ)=semiversin(π2−θ)=coversin(θ)2{\displaystyle {\textrm {semicoversin}}(\theta )={\textrm {semiversin}}\left({\frac {\pi }{2}}-\theta \right)={\frac {{\textrm {coversin}}(\theta )}{2}}}