The origins and etymology of the term are uncertain, although Cornish and East Anglican roots have been offered. Freely translated, 'shenanigans' means deception by trickery, silly antics, playing games, practical jokes and all in all just messing about. It sounds Irish in origin to me. Grandmother used sometimes usually with a tinge of humor, 'Arrrah! What shenanigans are they up to now?' other times she used it when she was quite vexed with someone, like 'That mister and his Shenanigans he'll have me worn before me time!'when Grandpa would use a toothpick out of the cup she kept them in on her kitchen dinette and then put it back in with all of the unused ones.
Most often this colloquialism is used in the plural form. I've heard her use shenanery which may be related. It's a cross between shenanigan and chicanery, used when someone has absolutely no idea about what is going on.
The word `shenanigans' first appeared in common vernaculars in California around the time the Gold Rush, but it wasn't used in print until 1855. Since then it has been spelled a numerous ways but most dictionaries today have decided to stick to this version.
Several word lists I checked with were in disagreement as to the origins, the majority opting for the conservative and ever popular phrase "origin unknown." Several experts deliberated its sources. Some claimed the word was derived from the East Anglican lingo nannicking in the sense of playing the fool. Another basis for the word was deduced from a likely link with the Spanish word chanada, a shortened form of charranada, meaning a trick or deceit, which, keeping California's history in mind could be an additional possible and plausible source. Nevertheless a further premise was used in 1948 in American Speech for the derivation from the German word schinnagel to indicate a nail that holds the rim to the wheel, which led to the German slang word schinageln, the peddler's jargon for "work, craft." Adding that the related colloquial verb chicanery was put together with Schenigelei, for a trick.
But in all likelihood it was another word brought over by the Irish from the Gaelic sionnachuighim for "I play the fox," which is to say, "I play tricks." It sounds Irish, and there certainly was no scarcity of Irishmen in the California mines, so it's conceivable to propose the Irish word sionnachuighm as the root.
Synonyms for shenanigans abound; paddy whacking, monkey business, horseplay, antics, capers, high jinks, silliness, silly season, vagary, whimsicality, banter, buffoonery, drollery, clowning, burlesque, farce, scrape, prank, trick, practical joke, mucking about and, skylarking; all pretty much get across the same idea of lively gobbledygook.
Accessed Oct 13 2002.