[′bes·əl i′lip‚soid əv ‚ā¦tēn¦fȯr·dē′wən] (geodesy) The reference ellipsoid of which the semimajor axis is 6,377,397.2 meters, the semiminor axis is 6,356,079.0 meters, and the flattening or ellipticity equals 1/299.15. Also known as Bessel spheroid of 1841.