Callithumpian refers to a band of discordant instruments or a noisy parade. It was first noted in America in 1836.
It’s possible it may have its origin in a southern English dialect word gallithumpian; the English Dialect Dictionary says this could refer to a heckler or someone who disturbs order at Parliamentary elections (which were then public events, not secret ballots). this probably derives from gally, “to frighten”, which turns up in another dialect word gallicrow for a scarecrow.
But it’s also been said to be a blend of calliope and thump, which sounds plausible as an evocation of a noisy fairground atmosphere, except that unfortunately calliope, in the sense of the steam-driven musical instrument, is not recorded before 1858.
The word survives, though it’s now rather regional even in the US, for example in the Callithumpian Parade on 4 July every year in Biwabik, Minnesota, and in the names of the Callithumpian Consort, which performs avant-garde music, and Jack Maheu’s Fire In The Pet Shop Callithumpian Jazz Band.
It has a second meaning in Australia and New Zealand, referring to some unspecified nonconformist religious sect. This may be derived from the other meaning given in the English Dialect Dictionary of “a group of social reformers”.