It's a nonce word and is used only in Finnegans Wake. Joyce intentionally made it long probably to catch readers' attention and persuade them to read his novel (Finnegans Wake).
It's defined by Your Dictionary as:
Bababadalgharaghtakamminarronnkonnbronntonnerronntuonnthunntrovarrhounawnskawntoohoohoordenenthurnuk: (nonce) A sound which represents the symbolic thunderclap associated with the fall of Adam and Eve.
A coinage from Finnegans Wake author James Joyce said to represent the thunderclap associated with the fall of Adam and Eve. The word is a hybrid of words in many languages that relate to thunder.
It took me a while to transcribe it (but I'm still unsure about the vowels).
Pronunciation (phonetic transcription):
From Interesting Literature:
Joyce uses the word Bababadalgharaghtakamminarronnkonnbronntonnerronntuonnthunntrovarrhounawnskawntoohoohoordenenthurnuk, which is meant to denote the symbolic thunderclap which accompanied the Fall of Adam and Eve (a meaning that is imbued with greater significance in light of Joyce’s lifelong fear of thunder).
It is a 101-letter word
that depicts the word for thunder in various languages.
There's a video on Adam Harvey's YouTube channel where he pronounces it himself and explains how to pronounce it.
He breaks it down into its constituent parts and explains what each word means and where it came from.
Here's the summary of his explanation:
- Bababadal: It's a reference to the tower of Babel (Genesis 11:1-9)
- gharaghta: (Hindi) karak, gargarahat, (Arabic) ra'd: thunder.
- kamminarronnkon: (Japanese) kaminari: thunder.
- bron: (Greek) brontê: thunder
- tonnerronn: (French) tonnerre: thunder.
- tuonn: (Italian) tuonno: thunder.
- thun: (English) thunder: thunder.
- trovarr: (Portuguese) trovão: thunder.
- hounawnskawn: (Swedish) åska, (Irish) scán: thunder
- toohoohoordenen (with a bit of a stutter): (Danish) torden: thunder
- thurnuk: (Irish) tórnach: thunder.
[Adam Harvey - YouTube]
It's also explained in Annotations to Finnegans Wake by Roland McHugh (Google Books).
Each word is explained at Finnegans Web.
The same explanation can also be found at Fweet.org:
Faction Paradox Wiki has also used it to refer to the blaring sound of a warship (I guess):
The Bababadalgharaghtakamminarronnkonnbronntonnerronntuonnthunntrovarrhounawnskawntoohoohoordenenthurnuk warships (also called planet-killer warships) were piloted by praxis-enabled posthumans from the Pilots' Coterie. The name came from James Joyce's Finnegans Wake, where it meant "a thunderclap so loud that it symbolises the Fall of Eden"....
There are 100+ pronunciations of this word (by people from different countries) on Pronounce Kiwi.