Shenanigans, or shenanigan, also with several variant spellings, can be dated to 1855 USA in both the OED and Etymonline, but the OED simply says "Origin obscure" and Etymonline throws a few guesses into the ring: Suggestions include Spanish chanada, a shortened form of charranada "trick, deceit;" or, less likely, German Schenigelei, peddler's ... More @Wikipedia
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