We don't have synonyms for swingletrees yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are swingletree, singletrees and singletree.
(n) :
Alternative form of singletree. [A bar behind draft animals and in front of a load, such as a wagon, that balances the load. Generally the animals are attached at the ends and the wagon or other load to a pivot in the middle of the singletree.]
(n) :
Alternative form of singletree. [A bar behind draft animals and in front of a load, such as a wagon, that balances the load. Generally the animals are attached at the ends and the wagon or other load to a pivot in the middle of the singletree.]