Pronunciation: (hwif'ul-trē", wif'-), [key]
—n. Northern U.S.
a crossbar, pivoted at the middle, to which the traces of a harness are fastened for pulling a cart, carriage, plow, etc. Also called whippletree, singletree, swingletree. Cf. doubletree.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.