contrapositive definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
Logic a proposition obtained by negating and transposing the terms of a given proposition: the contrapositive of “All A is B” is “All not-B is not-A”
contrapositive definition by American Heritage Dictionary
A proposition derived by negating and permuting the terms of another, equivalent proposition; for example, All not-Y is not-X is the contrapositive of All X is Y.