- Needn't is defined as need not.
An example of the usage of needn't is, "You needn't buy any more bread; we have plenty here."
needn't 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.
need not; do not need to or does not need to
needn't definition by American Heritage Dictionary
Contraction of need not.