The crossword solution for the term 'PREFIX IN PLANEDOM' is AERO, which is a four-letter word. AERO is a prefix that is commonly used in the aviation industry to refer to aircraft and other related topics. It is derived from the Greek word aer, meaning air or atmosphere. The prefix is often used in the names of aircraft, such as the Boeing 787 Dreamliner, and in the names of aviation-related organizations, such as the International Air Transport Association.