- The definition of a singletree is a bar between the pulling animal and the wagon or plow that balances the weight being pulled.
An example of a singletree is a metal crossbar between a horse and a buggy.
singletree definition by Webster's New World
Origin: altered (as if ; from single) ; from swingletree ; from Middle English swingle, rod, whip plush tre, tree
singletree definition by American Heritage Dictionary
Origin: Alteration (influenced by doubletree) of swingletree.