noun \??p??mp\Medical Definition of PUMP1: a device that raises, transfers, or compresses fluids or that attenuates gases especially by suction or pressure or both 2: heart 3: an act or the process of pumping 4: an energy source (as light) for pumping atoms or molecules 5: a mechanism by which atoms, ions, or molecules are transported across cell membranes???see proton pump, sodium pump Learn More