1: the act or an instance of regressing 2: a trend or shift toward a lower or less perfect state: as a: progressive decline of a manifestation of disease b (1): gradual loss of differentiation and function by a body part especially as a physiological change accompanying aging (2): gradual loss of memories and acquired skills c: reversion to an earlier mental or behavioral level d: a functional relationship between two or more correlated variables that is often empirically determined from data and is used especially to predict values of one variable when given values of the others <the regression of y on x is linear>; specifically: a function that yields the mean value of a random variable under the condition that one or more independent variables have specified values 3: retrograde motion
