The term 'Automatic, as a reaction' can be summarized by two crossword solutions: REFLEX (6 letters) and kneejerk (8 letters). REFLEX is an involuntary, automatic response to a stimulus, such as a reflexive action or reflexive behavior. Kneejerk is a type of REFLEX that is characterized by an immediate, involuntary response to a stimulus. It is usually associated with the knee jerk REFLEX, which is a reflexive contraction of the quadriceps muscle when the patellar tendon is tapped. Both REFLEX and kneejerk are examples of automatic reactions that occur without conscious thought.