n. (pl.epiphenomena) a mere by-product of a process that has no effect on the process itself. The term is used most frequently to refer to mental events considered as products of brain processes. Thus, though mental events are real in some sense, they are not real in the same way that biological states and events are real, and not necessary to the explanation of mental events themselves. Epiphenomena are conceived of as having no causal power. See epiphenomenalism. —epiphenomenaladj.