either of the two shafts between which a horse is hitched to a wagon
Webster’s New World College Dictionary, Fourth Edition, compiled by the
editors of Webster’s New World Dictionaries. Copyright © 2010 by Houghton
Mifflin Harcourt. Published by Houghton Mifflin Harcourt. All rights reserved.
Word origin of 'thill'ME thille, a stake, pole, plank < OE, akin to ON thil, OHG dil, board wall, plank floor < IE base *telo-, flat surface > L tellus, earth