Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio.
Informal a gradual decrease in nuclear weapons, armed forces, etc., esp. by an agreement in which a smaller number of newer weapons would replace older ones
Used by arrangement with John Wiley & Sons, Inc.
build-down - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Reduce, diminish, as in Owing to increased vigilance, traffic in narcotics is finally building down. This term, the antonym of build up, came into use about 1980 with regard to reducing the stockpile of nuclear weapons and soon was applied more widely.