1.NounA wind whose direction and speed are determined by a balance of the horizontal pressure gradient force and the force due to the earth's rotation to the left in the northern hemisphere and to the right in the southern hemisphere.
2.NounThat horizontal wind velocity for which the Coriolis force exactly balances the horizontal pressure gradient force. The geostrophic wind is thus directed along the contour lines on a constant-pressure surface (or along the isobars in a geopotential surface) with low elevations (or low pressure) to the left in the northern hemisphere and to the right in the southern hemisphere.