The term 'Plane Prefix' refers to the prefixes used in the names of aircraft. The two solutions for this term are AERO (4 letters) and MONO (4 letters). AERO is derived from the Greek word aer, meaning air, and is commonly used in the names of aircraft, such as the Aerospatiale-BAC Concorde. MONO is derived from the Greek word monos, meaning single, and is often used to refer to single-engine aircraft, such as the Monocoupe 90A.