From Gurunet:
horn·swog·gle (hôrn'swŏg'əl)
tr.v. Chiefly Northern & Western U.S., -gled, -gling, -gles.

To bamboozle; deceive.

[Origin unknown.]

Our Living Language We do not know the origin of hornswoggle. We do know that it belongs to a group of “fancified” words that were particularly popular in the American West in the 19th century. Hornswoggle is one of the earliest, first appearing around 1829. It is possible that these words were invented to poke fun at the more “sophisticated” East. Some other words of this ilk are absquatulate, also first appearing in the 1820s, skedaddle, first attested in 1861 in Missouri, and discombobulate, first recorded in 1916.