Final answer:
The brevity code word for 'Mode IV IFF' is Prowords, which is used in military communication to describe a secure identification system for friendly aircraft.
Step-by-step explanation:
The brevity code word meaning "Mode IV IFF" is Prowords. This term is typically used in military communication contexts where maintaining radio discipline and brevity is crucial. IFF stands for Identification, Friend or Foe, which is an electronic system designed to identify and track friendly aircraft and distinguish them from potential threats. Mode IV refers to a secure mode of IFF. In practice, specific code words for procedures and systems like IFF are established to enable quick and unambiguous communication among military personnel.