epiphenomenon

1. (philosophy, psychology) A mental process or state that is an incidental by-product of physiological events in the brain or nervous system.Examples: "It is a necessary corollary of the view here advanced that in instinct as such consciousness is a mere epiphenomenon—a by-product, with no bearing whatever on the performance of the activity in so far as it is instinctive."; "According to this hypothesis, mind is a ‘collateral product’ of the physical, an ‘epiphænomenon’ accompanying, but never causally affecting, the physical series of phænomena."; "From the monistic standpoint there is a choice between two possible alternatives; either consciousness is a form of energy, like heat, etc., or it is merely a so-called epiphenomenon. […] It is essential to have a clear notion of what is meant by an epiphenomenon. […] It designates an accompanying incident of a process which is assumed to have no causal relation to the further development of the process. […] For many years I have tried to recognize some actual idea underneath the epiphenomenon hypothesis of consciousness, but it more and more seems clear to me that there is no idea at all, and that the hypothesis is an empty phrase, a subterfuge, which really amounts only to this—we can explain consciousness very easily by merely assuming that it does not require to be explained at all."

2. (pathology) A symptom that develops during the course of a disease that is not connected to the disease.Examples: "EPIPHÆNOMENA, […] Signs in Diſeaſes which appear afterwards."; "The appetite commonly remains little impaired, but it is conjoined with the fear of taking food. The tongue is generally clean, and the taste natural; a contrary state the author considers and denominates an epiphenomenon."; "In all cases, the presence of bile in the blood is a mere epiphænomenon, and therefore demands no special attention."