—v.
1 intr. move backwards, esp. (in abstract senses) return to a former state.
2 intr. & tr. Psychol. return or cause to return mentally to a former stage of life, esp. through hypnosis or mental illness.
—n.
1 the act or an instance of going back.
2 reasoning from effect to cause.
Etymology: ME (as n.) f. L regressus f. regredi regress- (as RE-, gradi step)
Useful english dictionary. 2012.