1. The act or process of deteriorating or declining: The sociologists noted the appearance of retrogression in the compassionate behavior of the population after the takeover of the government by right wing patriots.
2. A return to a former and to a less complex level of development or organization: The marine biologists were astonished to note the retrogression in many of the smaller life forms in their study of tidal pool organisms over a period of many years.
3. Etymology: from Latin retrogressus, past participle of retrogradi, "to move backward"; from retro-, "backward" + gradi, "to go, to step".