Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio.
any person with whom a professional boxer spars or practices while training
Used by arrangement with John Wiley & Sons, Inc.
sparring partner - 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.
An individual with whom one enjoys arguing, as in Jim's my best sparring partner. This expression alludes to boxing, where since about 1900 it has denoted the person one practices or trains with. [Mid-1900s] Also see spar with.