doubletreeU.S.|ˈdʌb(ə)ltriː| [f. double a. + tree n., after U.S.single-tree= swingle-tree.] The cross-piece to which the swingle-tree of a carriage, plough, etc. is attached. 1847[see single-tree].1952Steinbeck East of Eden xiii. 121, I saw him..take the double-tree off the hay rake.