ETYM Latin regressio: cf. French régression.
1. A defense mechanism in which one flees from reality by assuming a more infantile state.
2. Returning to a former state; SYN. regress, reversion, retrogression, retroversion.
3. The relation between selected values of x and observed values of y (from which the most probable value of y can be predicted for any value of x); SYN. simple regression, regression toward the mean.
A word invented (usually unwittingly by subtracting an affix) on the assumption that a familiar word derives from it.