Needn't is defined as need not.contraction
An example of the usage of needn't is, "You needn't buy any more bread; we have plenty here."YourDictionary definition and usage example. Copyright © 2013 by LoveToKnow Corp.
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio.
need not; do not need to or does not need to
Used by arrangement with John Wiley & Sons, Inc.
The American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Contraction of need not.