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Webster 1913 Edition
Singletree
Sin′gle-treeˊ
,Noun.
[Cf.
Swingletree
.] The pivoted or swinging bar to which the traces of a harnessed horse are fixed; a whiffletree.
☞ When two horses draw abreast, a singletree is fixed at each end of another crosspiece, called the doubletree.