The term 'prefix for form' can be solved by two crossword solutions: AERI (4 letters) and UNI (3 letters). AERI is a prefix derived from the Greek word aer, meaning air. It is used to describe something that is related to air or atmosphere, such as aerospace or aerodynamics. UNI is a prefix derived from the Latin word unus, meaning one. It is used to describe something that is singular or unified, such as unicycle or uniform.