1) go-devil 2) pig a spherical, cylindrical or dumb-bell shaped object used to clean the internal surface of a pipeline, to propel liquids or separate different fluids, or to record the condition of the pipeline GRM: n. (1,2) Note: pigs can be propelled through a pipeline by air, gas or liquid under pressure, and are inserted into the pipeline by means of a device called a pig launcher and propelled through the line by fluid pressure