regress

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To return to a previous, usually worse or less developed state.
• intransitive verb To have a tendency to approach or go back to a statistical mean.
• intransitive verb To move backward or away from a reference point; recede.
• intransitive verb To induce a state of regression in.
• noun The act of regressing, especially the returning to a previous, usually worse or less developed state.
• noun The act of reasoning backward from an effect to a cause or of continually applying a process of reasoning to its own results.

from The Century Dictionary.

• To go back; return to a former place or state.
• In astronomy, to move from east toward west.
• noun Passage back; return.
• noun The power or liberty of returning or passing back.
• noun In Scots law, reëntry.
• noun In canon law. See access, 7.
• noun In logic, the passage in thought from effect to cause.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of passing back; passage back; return; retrogression. “The progress or regress of man”.
• noun The power or liberty of passing back.
• intransitive verb To go back; to return to a former place or state.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The act of passing back; passage back; return; retrogression.
• noun The power or liberty of passing back.
• verb intransitive To move backwards to an earlier stage; to devolve.
• verb transitive, statistics To perform a regression on an explanatory variable.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the reasoning involved when you assume the conclusion is true and reason backward to the evidence
• verb go back to a statistical means
• verb go back to bad behavior
• noun returning to a former state
• verb get worse or fall back to a previous condition
• verb go back to a previous state