RX-1 GND was printed on both the labels of substance CR 481516-23 42 and on the glue flask in the Staff. The meaning of the name is unknown.
Rx is an abbreviation for the Latin word "recipe", which = "take" (imperative), used in the pharmaceutical industry for medications and drugs. In electronics Rx means 'Receiver', which when added to GND you get 'Receiver(1)- Ground'
GND is a common abbreviation for 'Ground' in electronics. This generally refers to the negative terminal of a (positive-voltage) power supply and is sometimes called the point of lowest potential in a circuit, though this may not necessarily be true for all circuits.