[‚sach·ə′rā·shən ¦ad·ē·ə¦bad·ik ′laps ‚rāt] (meteorology) A special case of process lapse rate, defined as the rate of decrease of temperature with height of an air parcel lifted in a saturation-adiabatic process through an atmosphere in hydrostatic equilibrium. Also known as moist-adiabatic lapse rate.