singletree [
'siŋgltri:]
n. 车前横木
Singletree \Sin"gle*tree`\, n. [Cf. {Swingletree}.]
The pivoted or swinging bar to which the traces of a
harnessed horse are fixed; a whiffletree.
Note: When two horses draw abreast, a singletree is fixed at
each end of another crosspiece, called the doubletree.