airhead: a bridgehead seized by airborne troops
bridgehead: an area in hostile territory that has been captured and is held awaiting further troops and supplies
systeme international d'unites: a complete metric system of units of measurement for scientists; fundamental quantities are length (meter) and mass (kilogram) and time (second) and electric current (ampere) and temperature (kelvin) and amount of matter (mole) and luminous intensity (candela)